Add NonNull annotations to Plugin and PluginFactory

src/org/kde/kdeconnect/Plugins/BatteryPlugin/BatteryPlugin.java

@@ -40,12 +40,12 @@ public class BatteryPlugin extends Plugin {
     private DeviceBatteryInfo remoteBatteryInfo;
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_battery);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_battery_desc);
     }
 
@@ -110,7 +110,7 @@ public class BatteryPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         if (np.getBoolean("request")) {
             device.sendPacket(batteryInfo);
@@ -139,12 +139,12 @@ public class BatteryPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_BATTERY_REQUEST, PACKET_TYPE_BATTERY};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_BATTERY_REQUEST, PACKET_TYPE_BATTERY};
     }
 

src/org/kde/kdeconnect/Plugins/BigscreenPlugin/BigscreenPlugin.java

@@ -17,6 +17,7 @@ import android.content.Intent;
 import android.graphics.drawable.Drawable;
 import android.view.KeyEvent;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.kde.kdeconnect.Device;
@@ -42,12 +43,12 @@ public class BigscreenPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getString(R.string.pref_plugin_bigscreen);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getString(R.string.pref_plugin_bigscreen_desc);
     }
 
@@ -79,19 +80,19 @@ public class BigscreenPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {  return new String[]{PACKET_TYPE_BIGSCREEN_STT}; }
+    public @NonNull String[] getSupportedPacketTypes() {  return new String[]{PACKET_TYPE_BIGSCREEN_STT}; }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_REQUEST, PACKET_TYPE_BIGSCREEN_STT};
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.pref_plugin_bigscreen);
     }
 
-    public String[] getOptionalPermissions() {
+    public @NonNull String[] getOptionalPermissions() {
         return new String[]{Manifest.permission.RECORD_AUDIO};
     }
 

src/org/kde/kdeconnect/Plugins/ClibpoardPlugin/ClipboardPlugin.java

@@ -18,6 +18,7 @@ import android.graphics.drawable.Drawable;
 import android.os.Build;
 import android.widget.Toast;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.kde.kdeconnect.NetworkPacket;
@@ -54,17 +55,17 @@ public class ClipboardPlugin extends Plugin {
     private final static String PACKET_TYPE_CLIPBOARD_CONNECT = "kdeconnect.clipboard.connect";
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_clipboard);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_clipboard_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         String content = np.getString("content");
         switch (np.getType()) {
             case (PACKET_TYPE_CLIPBOARD):
@@ -114,17 +115,17 @@ public class ClipboardPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_CLIPBOARD, PACKET_TYPE_CLIPBOARD_CONNECT};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_CLIPBOARD, PACKET_TYPE_CLIPBOARD_CONNECT};
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.send_clipboard);
     }
 

src/org/kde/kdeconnect/Plugins/ConnectivityReportPlugin/ConnectivityReportPlugin.java

@@ -16,6 +16,7 @@ import android.telephony.SubscriptionManager.OnSubscriptionsChangedListener;
 import android.telephony.TelephonyManager;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 
 import org.json.JSONException;
@@ -70,12 +71,12 @@ public class ConnectivityReportPlugin extends Plugin {
     private final HashMap<Integer, SubscriptionState> states = new HashMap<>();
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_connectivity_report);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_connectivity_report_desc);
     }
 
@@ -228,7 +229,7 @@ public class ConnectivityReportPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         if (PACKET_TYPE_CONNECTIVITY_REPORT_REQUEST.equals(np.getType())) {
             Log.i("ConnectivityReport", "Requested");
             serializeSignalStrengths();
@@ -239,17 +240,17 @@ public class ConnectivityReportPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_CONNECTIVITY_REPORT_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_CONNECTIVITY_REPORT};
     }
 
     @Override
-    public String[] getRequiredPermissions() {
+    public @NonNull String[] getRequiredPermissions() {
         return new String[]{
                 Manifest.permission.READ_PHONE_STATE,
         };

src/org/kde/kdeconnect/Plugins/ContactsPlugin/ContactsPlugin.java

@@ -12,6 +12,8 @@ package org.kde.kdeconnect.Plugins.ContactsPlugin;
 import android.Manifest;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
+
 import org.kde.kdeconnect.Helpers.ContactsHelper;
 import org.kde.kdeconnect.Helpers.ContactsHelper.ContactNotFoundException;
 import org.kde.kdeconnect.Helpers.ContactsHelper.VCardBuilder;
@@ -66,17 +68,17 @@ public class ContactsPlugin extends Plugin {
     private static final String PACKET_TYPE_CONTACTS_RESPONSE_VCARDS = "kdeconnect.contacts.response_vcards";
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_contacts);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_contacts_desc);
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{
                 PACKET_TYPE_CONTACTS_REQUEST_ALL_UIDS_TIMESTAMPS,
                 PACKET_TYPE_CONTACTS_REQUEST_VCARDS_BY_UIDS
@@ -84,7 +86,7 @@ public class ContactsPlugin extends Plugin {
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{
                 PACKET_TYPE_CONTACTS_RESPONSE_UIDS_TIMESTAMPS,
                 PACKET_TYPE_CONTACTS_RESPONSE_VCARDS
@@ -102,7 +104,7 @@ public class ContactsPlugin extends Plugin {
     }
 
     @Override
-    public String[] getRequiredPermissions() {
+    public @NonNull String[] getRequiredPermissions() {
         return new String[]{Manifest.permission.READ_CONTACTS};
         // One day maybe we will also support WRITE_CONTACTS, but not yet
     }
@@ -214,7 +216,7 @@ public class ContactsPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         switch (np.getType()) {
             case PACKET_TYPE_CONTACTS_REQUEST_ALL_UIDS_TIMESTAMPS:
                 return this.handleRequestAllUIDsTimestamps(np);

src/org/kde/kdeconnect/Plugins/FindMyPhonePlugin/FindMyPhonePlugin.java

@@ -20,6 +20,7 @@ import android.preference.PreferenceManager;
 import android.provider.Settings;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.core.app.NotificationCompat;
 import androidx.core.content.ContextCompat;
 
@@ -47,7 +48,7 @@ public class FindMyPhonePlugin extends Plugin {
     private PowerManager powerManager;
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         switch (DeviceHelper.getDeviceType(context)) {
             case Tv:
                 return context.getString(R.string.findmyphone_title_tv);
@@ -60,7 +61,7 @@ public class FindMyPhonePlugin extends Plugin {
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getString(R.string.findmyphone_description);
     }
 
@@ -106,7 +107,7 @@ public class FindMyPhonePlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q || LifecycleHelper.isInForeground()) {
             Intent intent = new Intent(context, FindMyPhoneActivity.class);
             intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
@@ -194,12 +195,12 @@ public class FindMyPhonePlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_FINDMYPHONE_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return ArrayUtils.EMPTY_STRING_ARRAY;
     }
 

src/org/kde/kdeconnect/Plugins/FindRemoteDevicePlugin/FindRemoteDevicePlugin.java

@@ -9,6 +9,8 @@ package org.kde.kdeconnect.Plugins.FindRemoteDevicePlugin;
 import android.app.Activity;
 import android.content.Context;
 
+import androidx.annotation.NonNull;
+
 import org.apache.commons.lang3.ArrayUtils;
 import org.kde.kdeconnect.NetworkPacket;
 import org.kde.kdeconnect.Plugins.FindMyPhonePlugin.FindMyPhonePlugin;
@@ -20,22 +22,22 @@ import org.kde.kdeconnect_tp.R;
 public class FindRemoteDevicePlugin extends Plugin {
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_findremotedevice);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_findremotedevice_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         return true;
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.ring);
     }
 
@@ -57,12 +59,12 @@ public class FindRemoteDevicePlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return ArrayUtils.EMPTY_STRING_ARRAY;
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{FindMyPhonePlugin.PACKET_TYPE_FINDMYPHONE_REQUEST};
     }
 }

src/org/kde/kdeconnect/Plugins/MousePadPlugin/MousePadPlugin.java

@@ -11,6 +11,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.graphics.drawable.Drawable;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.kde.kdeconnect.NetworkPacket;
@@ -29,7 +30,7 @@ public class MousePadPlugin extends Plugin {
     private boolean keyboardEnabled = true;
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         keyboardEnabled = np.getBoolean("state", true);
 
@@ -37,12 +38,12 @@ public class MousePadPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getString(R.string.pref_plugin_mousepad);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getString(R.string.pref_plugin_mousepad_desc);
     }
 
@@ -74,17 +75,17 @@ public class MousePadPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_KEYBOARDSTATE};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_REQUEST};
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.open_mousepad);
     }
 

src/org/kde/kdeconnect/Plugins/MouseReceiverPlugin/MouseReceiverPlugin.java

@@ -10,9 +10,11 @@ import android.os.Build;
 import android.provider.Settings;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 import androidx.fragment.app.DialogFragment;
 
+import org.apache.commons.lang3.ArrayUtils;
 import org.kde.kdeconnect.NetworkPacket;
 import org.kde.kdeconnect.Plugins.Plugin;
 import org.kde.kdeconnect.Plugins.RemoteKeyboardPlugin.RemoteKeyboardPlugin;
@@ -37,7 +39,7 @@ public class MouseReceiverPlugin extends Plugin {
     }
 
     @Override
-    public DialogFragment getPermissionExplanationDialog() {
+    public @NonNull DialogFragment getPermissionExplanationDialog() {
         return new StartActivityAlertDialogFragment.Builder()
                 .setTitle(R.string.mouse_receiver_plugin_description)
                 .setMessage(R.string.mouse_receiver_no_permissions)
@@ -50,7 +52,7 @@ public class MouseReceiverPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         if (!np.getType().equals(PACKET_TYPE_MOUSEPAD_REQUEST)) {
             Log.e("MouseReceiverPlugin", "Invalid packet type for MouseReceiverPlugin: " + np.getType());
             return false;
@@ -126,22 +128,22 @@ public class MouseReceiverPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getString(R.string.mouse_receiver_plugin_name);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getString(R.string.mouse_receiver_plugin_description);
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
-        return new String[0];
+        return ArrayUtils.EMPTY_STRING_ARRAY;
     }
 }

src/org/kde/kdeconnect/Plugins/MprisPlugin/MprisPlugin.java

@@ -13,6 +13,7 @@ import android.graphics.Bitmap;
 import android.graphics.drawable.Drawable;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.kde.kdeconnect.NetworkPacket;
@@ -239,12 +240,12 @@ public class MprisPlugin extends Plugin {
     private final ConcurrentHashMap<String, Callback> playerListUpdated = new ConcurrentHashMap<>();
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_mpris);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_mpris_desc);
     }
 
@@ -305,7 +306,7 @@ public class MprisPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         if (np.getBoolean("transferringAlbumArt", false)) {
             AlbumArtCache.payloadToDiskCache(np.getString("albumArtUrl"), np.getPayload());
             return true;
@@ -405,12 +406,12 @@ public class MprisPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_MPRIS};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_MPRIS_REQUEST};
     }
 
@@ -493,7 +494,7 @@ public class MprisPlugin extends Plugin {
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.open_mpris_controls);
     }
 

src/org/kde/kdeconnect/Plugins/MprisReceiverPlugin/MprisReceiverPlugin.java

@@ -15,6 +15,7 @@ import android.os.Looper;
 import android.provider.Settings;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
 import androidx.core.content.ContextCompat;
@@ -86,17 +87,17 @@ public class MprisReceiverPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_mprisreceiver);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_mprisreceiver_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         if (np.getBoolean("requestPlayerList")) {
             sendPlayerList();
@@ -158,12 +159,12 @@ public class MprisReceiverPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_MPRIS_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_MPRIS};
     }
 
@@ -233,7 +234,7 @@ public class MprisReceiverPlugin extends Plugin {
     }
 
     @Override
-    public DialogFragment getPermissionExplanationDialog() {
+    public @NonNull DialogFragment getPermissionExplanationDialog() {
         return new StartActivityAlertDialogFragment.Builder()
                 .setTitle(R.string.pref_plugin_mpris)
                 .setMessage(R.string.no_permission_mprisreceiver)

src/org/kde/kdeconnect/Plugins/NotificationsPlugin/NotificationsPlugin.java

@@ -82,12 +82,12 @@ public class NotificationsPlugin extends Plugin implements NotificationReceiver.
     private KeyguardManager keyguardManager;
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_notifications);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_notifications_desc);
     }
 
@@ -555,7 +555,7 @@ public class NotificationsPlugin extends Plugin implements NotificationReceiver.
     }
 
     @Override
-    public DialogFragment getPermissionExplanationDialog() {
+    public @NonNull DialogFragment getPermissionExplanationDialog() {
         return new StartActivityAlertDialogFragment.Builder()
                 .setTitle(R.string.pref_plugin_notifications)
                 .setMessage(R.string.no_permissions)
@@ -568,12 +568,12 @@ public class NotificationsPlugin extends Plugin implements NotificationReceiver.
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_NOTIFICATION_REQUEST, PACKET_TYPE_NOTIFICATION_REPLY, PACKET_TYPE_NOTIFICATION_ACTION};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_NOTIFICATION};
     }
 

src/org/kde/kdeconnect/Plugins/PhotoPlugin/PhotoPlugin.java

@@ -11,6 +11,7 @@ import android.content.Intent;
 import android.graphics.drawable.Drawable;
 import android.net.Uri;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.kde.kdeconnect.Helpers.FilesHelper;
@@ -26,17 +27,17 @@ public class PhotoPlugin extends Plugin {
     private final static String PACKET_TYPE_PHOTO_REQUEST = "kdeconnect.photo.request";
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.take_picture);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.plugin_photo_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         Intent intent = new Intent(context, PhotoActivity.class);
         intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
         intent.putExtra("deviceId", device.getDeviceId());
@@ -62,12 +63,12 @@ public class PhotoPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_PHOTO_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_PHOTO};
     }
 

src/org/kde/kdeconnect/Plugins/PingPlugin/PingPlugin.java

@@ -14,6 +14,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.core.app.NotificationCompat;
 import androidx.core.content.ContextCompat;
 
@@ -30,17 +31,17 @@ public class PingPlugin extends Plugin {
     private final static String PACKET_TYPE_PING = "kdeconnect.ping";
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_ping);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_ping_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         if (!np.getType().equals(PACKET_TYPE_PING)) {
             Log.e("PingPlugin", "Ping plugin should not receive packets other than pings!");
@@ -86,7 +87,7 @@ public class PingPlugin extends Plugin {
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.send_ping);
     }
 
@@ -108,12 +109,12 @@ public class PingPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_PING};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_PING};
     }
 

src/org/kde/kdeconnect/Plugins/Plugin.java

@@ -21,6 +21,7 @@ import androidx.core.content.ContextCompat;
 import androidx.fragment.app.DialogFragment;
 
 import org.apache.commons.lang3.ArrayUtils;
+import org.jetbrains.annotations.NotNull;
 import org.kde.kdeconnect.Device;
 import org.kde.kdeconnect.NetworkPacket;
 import org.kde.kdeconnect.UserInterface.AlertDialogFragment;
@@ -44,7 +45,7 @@ public abstract class Plugin {
         }
     }
 
-    public String getSharedPreferencesName() {
+    public @NotNull String getSharedPreferencesName() {
         if (device == null) {
             throw new RuntimeException("You have to call setContext() before you can call getSharedPreferencesName()");
         }
@@ -55,8 +56,7 @@ public abstract class Plugin {
             return this.getPluginKey() + "_preferences";
     }
 
-    @Nullable
+    public @Nullable SharedPreferences getPreferences() {
-    public SharedPreferences getPreferences() {
         return this.preferences;
     }
 
@@ -64,7 +64,7 @@ public abstract class Plugin {
      * To receive the network packet from the unpaired device, override
      * listensToUnpairedDevices to return true and this method.
      */
-    public boolean onUnpairedDevicePacketReceived(NetworkPacket np) {
+    public boolean onUnpairedDevicePacketReceived(@NonNull NetworkPacket np) {
         return false;
     }
 
@@ -80,11 +80,11 @@ public abstract class Plugin {
      * Return the internal plugin name, that will be used as a
      * unique key to distinguish it. Use the class name as key.
      */
-    public String getPluginKey() {
+    public final @NonNull String getPluginKey() {
         return getPluginKey(this.getClass());
     }
 
-    public static String getPluginKey(Class<? extends Plugin> p) {
+    public static @NonNull String getPluginKey(Class<? extends Plugin> p) {
         return p.getSimpleName();
     }
 
@@ -92,19 +92,19 @@ public abstract class Plugin {
      * Return the human-readable plugin name. This function can
      * access this.context to provide translated text.
      */
-    public abstract String getDisplayName();
+    public abstract @NonNull String getDisplayName();
 
     /**
      * Return the human-readable description of this plugin. This
      * function can access this.context to provide translated text.
      */
-    public abstract String getDescription();
+    public abstract @NonNull String getDescription();
 
     /**
      * Return the action name displayed in the main activity, that
      * will call startMainActivity when clicked
      */
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return getDisplayName();
     }
 
@@ -112,7 +112,7 @@ public abstract class Plugin {
      * Return an icon associated to this plugin. This function can
      * access this.context to load the image from resources.
      */
-    public Drawable getIcon() {
+    public @Nullable Drawable getIcon() {
         return null;
     }
 
@@ -148,7 +148,7 @@ public abstract class Plugin {
      *
      * @return The PluginSettingsFragment used to display this plugins settings
      */
-    public PluginSettingsFragment getSettingsFragment(Activity activity) {
+    public @Nullable PluginSettingsFragment getSettingsFragment(Activity activity) {
         throw new RuntimeException("Plugin doesn't reimplement getSettingsFragment: " + getPluginKey());
 
     }
@@ -216,25 +216,25 @@ public abstract class Plugin {
      * when we have done something in response to the packet or false
      * otherwise, even though that value is unused as of now.
      */
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         return false;
     }
 
     /**
      * Should return the list of NetworkPacket types that this plugin can handle
      */
-    public abstract String[] getSupportedPacketTypes();
+    public abstract @NonNull String[] getSupportedPacketTypes();
 
     /**
      * Should return the list of NetworkPacket types that this plugin can send
      */
-    public abstract String[] getOutgoingPacketTypes();
+    public abstract @NonNull String[] getOutgoingPacketTypes();
 
     /**
      * Should return the list of permissions from Manifest.permission.* that, if not present,
      * mean the plugin can't be loaded.
      */
-    protected String[] getRequiredPermissions() {
+    protected @NonNull String[] getRequiredPermissions() {
         return ArrayUtils.EMPTY_STRING_ARRAY;
     }
 
@@ -242,7 +242,7 @@ public abstract class Plugin {
      * Should return the list of permissions from Manifest.permission.* that enable additional
      * functionality in the plugin (without preventing the plugin to load).
      */
-    protected String[] getOptionalPermissions() {
+    protected @NonNull String[] getOptionalPermissions() {
         return ArrayUtils.EMPTY_STRING_ARRAY;
     }
 
@@ -261,12 +261,12 @@ public abstract class Plugin {
     }
 
     //Permission from Manifest.permission.*
-    protected boolean isPermissionGranted(String permission) {
+    protected boolean isPermissionGranted(@NonNull String permission) {
         int result = ContextCompat.checkSelfPermission(context, permission);
         return (result == PackageManager.PERMISSION_GRANTED);
     }
 
-    private boolean arePermissionsGranted(String[] permissions) {
+    private boolean arePermissionsGranted(@NonNull String[] permissions) {
         for (String permission : permissions) {
             if (!isPermissionGranted(permission)) {
                 return false;
@@ -275,7 +275,7 @@ public abstract class Plugin {
         return true;
     }
 
-    private PermissionsAlertDialogFragment requestPermissionDialog(final String[] permissions, @StringRes int reason) {
+    private @NonNull PermissionsAlertDialogFragment requestPermissionDialog(@NonNull final String[] permissions, @StringRes int reason) {
         return new PermissionsAlertDialogFragment.Builder()
                 .setTitle(getDisplayName())
                 .setMessage(reason)
@@ -291,11 +291,11 @@ public abstract class Plugin {
      * the problem (and how to fix it, if possible) to the user.
      */
 
-    public DialogFragment getPermissionExplanationDialog() {
+    public @NonNull DialogFragment getPermissionExplanationDialog() {
         return requestPermissionDialog(getRequiredPermissions(), getPermissionExplanation());
     }
 
-    public AlertDialogFragment getOptionalPermissionExplanationDialog() {
+    public @NonNull AlertDialogFragment getOptionalPermissionExplanationDialog() {
         return requestPermissionDialog(getOptionalPermissions(), getOptionalPermissionExplanation());
     }
 

src/org/kde/kdeconnect/Plugins/PluginFactory.java

@@ -6,13 +6,15 @@
 
 package org.kde.kdeconnect.Plugins;
 
-import static org.apache.commons.collections4.SetUtils.emptyIfNull;
 import static org.apache.commons.collections4.SetUtils.unmodifiableSet;
 
 import android.content.Context;
 import android.graphics.drawable.Drawable;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import org.atteo.classindex.ClassIndex;
 import org.atteo.classindex.IndexAnnotated;
 import org.kde.kdeconnect.Device;
@@ -27,7 +29,7 @@ import java.util.concurrent.ConcurrentHashMap;
 
 public class PluginFactory {
 
-    public static void sortPluginList(List<String> plugins) {
+    public static void sortPluginList(@NonNull List<String> plugins) {
         plugins.sort(Comparator.comparing(o -> pluginInfo.get(o).displayName));
     }
 
@@ -36,10 +38,10 @@ public class PluginFactory {
 
     public static class PluginInfo {
 
-        PluginInfo(String displayName, String description, Drawable icon,
+        PluginInfo(@NonNull String displayName, @NonNull String description, @Nullable Drawable icon,
                    boolean enabledByDefault, boolean hasSettings, boolean supportsDeviceSpecificSettings,
-                   boolean listenToUnpaired, String[] supportedPacketTypes, String[] outgoingPacketTypes,
+                   boolean listenToUnpaired, @NonNull String[] supportedPacketTypes, @NonNull String[] outgoingPacketTypes,
-                   Class<? extends Plugin> instantiableClass) {
+                   @NonNull Class<? extends Plugin> instantiableClass) {
             this.displayName = displayName;
             this.description = description;
             this.icon = icon;
@@ -47,20 +49,20 @@ public class PluginFactory {
             this.hasSettings = hasSettings;
             this.supportsDeviceSpecificSettings = supportsDeviceSpecificSettings;
             this.listenToUnpaired = listenToUnpaired;
-            this.supportedPacketTypes = emptyIfNull(unmodifiableSet(supportedPacketTypes));
+            this.supportedPacketTypes = unmodifiableSet(supportedPacketTypes);
-            this.outgoingPacketTypes = emptyIfNull(unmodifiableSet(outgoingPacketTypes));
+            this.outgoingPacketTypes = unmodifiableSet(outgoingPacketTypes);
             this.instantiableClass = instantiableClass;
         }
 
-        public String getDisplayName() {
+        public @NonNull String getDisplayName() {
             return displayName;
         }
 
-        public String getDescription() {
+        public @NonNull String getDescription() {
             return description;
         }
 
-        public Drawable getIcon() {
+        public @Nullable Drawable getIcon() {
             return icon;
         }
 
@@ -90,15 +92,15 @@ public class PluginFactory {
             return instantiableClass;
         }
 
-        private final String displayName;
+        private final @NonNull String displayName;
-        private final String description;
+        private final @NonNull String description;
-        private final Drawable icon;
+        private final @Nullable Drawable icon;
         private final boolean enabledByDefault;
         private final boolean hasSettings;
         private final boolean supportsDeviceSpecificSettings;
         private final boolean listenToUnpaired;
-        private final Set<String> supportedPacketTypes;
+        private final @NonNull Set<String> supportedPacketTypes;
-        private final Set<String> outgoingPacketTypes;
+        private final @NonNull Set<String> outgoingPacketTypes;
         private final Class<? extends Plugin> instantiableClass;
 
     }
@@ -126,11 +128,11 @@ public class PluginFactory {
         Log.i("PluginFactory","Loaded "+pluginInfo.size()+" plugins");
     }
 
-    public static Set<String> getAvailablePlugins() {
+    public static @NonNull Set<String> getAvailablePlugins() {
         return pluginInfo.keySet();
     }
 
-    public static Plugin instantiatePluginForDevice(Context context, String pluginKey, Device device) {
+    public static @Nullable Plugin instantiatePluginForDevice(Context context, String pluginKey, Device device) {
         PluginInfo info = pluginInfo.get(pluginKey);
         try {
             Plugin plugin = info.getInstantiableClass().newInstance();
@@ -142,7 +144,7 @@ public class PluginFactory {
         }
     }
 
-    public static Set<String> getIncomingCapabilities() {
+    public static @NonNull Set<String> getIncomingCapabilities() {
         HashSet<String> capabilities = new HashSet<>();
         for (PluginInfo plugin : pluginInfo.values()) {
             capabilities.addAll(plugin.getSupportedPacketTypes());
@@ -150,7 +152,7 @@ public class PluginFactory {
         return capabilities;
     }
 
-    public static Set<String> getOutgoingCapabilities() {
+    public static @NonNull Set<String> getOutgoingCapabilities() {
         HashSet<String> capabilities = new HashSet<>();
         for (PluginInfo plugin : pluginInfo.values()) {
             capabilities.addAll(plugin.getOutgoingPacketTypes());
@@ -158,7 +160,7 @@ public class PluginFactory {
         return capabilities;
     }
 
-    public static Set<String> pluginsForCapabilities(Set<String> incoming, Set<String> outgoing) {
+    public static @NonNull Set<String> pluginsForCapabilities(Set<String> incoming, Set<String> outgoing) {
         HashSet<String> plugins = new HashSet<>();
         for (Map.Entry<String, PluginInfo> entry : pluginInfo.entrySet()) {
             String pluginId = entry.getKey();

src/org/kde/kdeconnect/Plugins/PresenterPlugin/PresenterPlugin.java

@@ -15,6 +15,7 @@ import android.content.Intent;
 import android.graphics.drawable.Drawable;
 import android.view.KeyEvent;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.apache.commons.lang3.ArrayUtils;
@@ -35,7 +36,7 @@ public class PresenterPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getString(R.string.pref_plugin_presenter);
     }
 
@@ -45,7 +46,7 @@ public class PresenterPlugin extends Plugin {
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getString(R.string.pref_plugin_presenter_desc);
     }
 
@@ -72,15 +73,15 @@ public class PresenterPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {  return ArrayUtils.EMPTY_STRING_ARRAY; }
+    public @NonNull String[] getSupportedPacketTypes() {  return ArrayUtils.EMPTY_STRING_ARRAY; }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_REQUEST, PACKET_TYPE_PRESENTER};
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.pref_plugin_presenter);
     }
 

src/org/kde/kdeconnect/Plugins/ReceiveNotificationsPlugin/ReceiveNotificationsPlugin.java

@@ -14,6 +14,7 @@ import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.core.app.NotificationCompat;
 import androidx.core.content.ContextCompat;
 
@@ -33,12 +34,12 @@ public class ReceiveNotificationsPlugin extends Plugin {
     private final static String PACKET_TYPE_NOTIFICATION_REQUEST = "kdeconnect.notification.request";
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_receive_notifications);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_receive_notifications_desc);
     }
 
@@ -113,12 +114,12 @@ public class ReceiveNotificationsPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_NOTIFICATION};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_NOTIFICATION_REQUEST};
     }
 }

src/org/kde/kdeconnect/Plugins/RemoteKeyboardPlugin/RemoteKeyboardPlugin.java

@@ -21,6 +21,7 @@ import android.view.inputmethod.ExtractedText;
 import android.view.inputmethod.ExtractedTextRequest;
 import android.view.inputmethod.InputConnection;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 import androidx.core.util.Pair;
 import androidx.fragment.app.DialogFragment;
@@ -143,12 +144,12 @@ public class RemoteKeyboardPlugin extends Plugin implements SharedPreferences.On
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getString(R.string.pref_plugin_remotekeyboard);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getString(R.string.pref_plugin_remotekeyboard_desc);
     }
 
@@ -173,12 +174,12 @@ public class RemoteKeyboardPlugin extends Plugin implements SharedPreferences.On
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_MOUSEPAD_ECHO, PACKET_TYPE_MOUSEPAD_KEYBOARDSTATE};
     }
 
@@ -361,7 +362,7 @@ public class RemoteKeyboardPlugin extends Plugin implements SharedPreferences.On
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         if (!np.getType().equals(PACKET_TYPE_MOUSEPAD_REQUEST)) {
             Log.e("RemoteKeyboardPlugin", "Invalid packet type for RemoteKeyboardPlugin: "+np.getType());
@@ -423,7 +424,7 @@ public class RemoteKeyboardPlugin extends Plugin implements SharedPreferences.On
     }
 
     @Override
-    public DialogFragment getPermissionExplanationDialog() {
+    public @NonNull DialogFragment getPermissionExplanationDialog() {
         return new StartActivityAlertDialogFragment.Builder()
                 .setTitle(R.string.pref_plugin_remotekeyboard)
                 .setMessage(R.string.no_permissions_remotekeyboard)

src/org/kde/kdeconnect/Plugins/RunCommandPlugin/RunCommandPlugin.java

@@ -15,6 +15,7 @@ import android.graphics.drawable.Drawable;
 import android.os.Build;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 import androidx.preference.PreferenceManager;
 
@@ -67,12 +68,12 @@ public class RunCommandPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_runcommand);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_runcommand_desc);
     }
 
@@ -89,7 +90,7 @@ public class RunCommandPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         if (np.has("commandList")) {
             commandList.clear();
@@ -150,12 +151,12 @@ public class RunCommandPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_RUNCOMMAND};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_RUNCOMMAND_REQUEST};
     }
 
@@ -184,7 +185,7 @@ public class RunCommandPlugin extends Plugin {
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.pref_plugin_runcommand);
     }
 

src/org/kde/kdeconnect/Plugins/SMSPlugin/SMSPlugin.java

@@ -30,6 +30,7 @@ import android.telephony.PhoneNumberUtils;
 import android.telephony.SmsManager;
 import android.telephony.SmsMessage;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import com.klinker.android.logger.Log;
@@ -374,17 +375,17 @@ public class SMSPlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_telepathy);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_telepathy_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         long subID;
 
         switch (np.getType()) {
@@ -559,7 +560,7 @@ public class SMSPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{
                 PACKET_TYPE_SMS_REQUEST,
                 TelephonyPlugin.PACKET_TYPE_TELEPHONY_REQUEST,
@@ -570,7 +571,7 @@ public class SMSPlugin extends Plugin {
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{
                 PACKET_TYPE_SMS_MESSAGE,
                 PACKET_TYPE_SMS_ATTACHMENT_FILE
@@ -578,7 +579,7 @@ public class SMSPlugin extends Plugin {
     }
 
     @Override
-    public String[] getRequiredPermissions() {
+    public @NonNull String[] getRequiredPermissions() {
         return new String[]{
                 Manifest.permission.SEND_SMS,
                 Manifest.permission.READ_SMS,

src/org/kde/kdeconnect/Plugins/SftpPlugin/SftpPlugin.java

@@ -49,12 +49,12 @@ public class SftpPlugin extends Plugin implements SharedPreferences.OnSharedPref
     private static final SimpleSftpServer server = new SimpleSftpServer();
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_sftp);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_sftp_desc);
     }
 
@@ -73,7 +73,7 @@ public class SftpPlugin extends Plugin implements SharedPreferences.OnSharedPref
     }
 
     @Override
-    public AlertDialogFragment getPermissionExplanationDialog() {
+    public @NonNull AlertDialogFragment getPermissionExplanationDialog() {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
             return new StartActivityAlertDialogFragment.Builder()
                     .setTitle(getDisplayName())
@@ -106,7 +106,7 @@ public class SftpPlugin extends Plugin implements SharedPreferences.OnSharedPref
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         if (np.getBoolean("startBrowsing")) {
             if (!server.isInitialized()) {
                 try {
@@ -219,12 +219,12 @@ public class SftpPlugin extends Plugin implements SharedPreferences.OnSharedPref
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_SFTP_REQUEST};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_SFTP};
     }
 

src/org/kde/kdeconnect/Plugins/SharePlugin/SharePlugin.java

@@ -79,7 +79,7 @@ public class SharePlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_sharereceiver);
     }
 
@@ -89,7 +89,7 @@ public class SharePlugin extends Plugin {
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_sharereceiver_desc);
     }
 
@@ -99,7 +99,7 @@ public class SharePlugin extends Plugin {
     }
 
     @Override
-    public String getActionName() {
+    public @NonNull String getActionName() {
         return context.getString(R.string.send_files);
     }
 
@@ -117,7 +117,7 @@ public class SharePlugin extends Plugin {
 
     @Override
     @WorkerThread
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
         try {
             if (np.getType().equals(PACKET_TYPE_SHARE_REQUEST_UPDATE)) {
                 if (receiveFileJob != null && receiveFileJob.isRunning()) {
@@ -279,17 +279,17 @@ public class SharePlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_SHARE_REQUEST, PACKET_TYPE_SHARE_REQUEST_UPDATE};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_SHARE_REQUEST};
     }
 
     @Override
-    public String[] getOptionalPermissions() {
+    public @NonNull String[] getOptionalPermissions() {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
             return ArrayUtils.EMPTY_STRING_ARRAY;
         } else {

src/org/kde/kdeconnect/Plugins/SystemVolumePlugin/SystemVolumePlugin.java

@@ -9,6 +9,8 @@ package org.kde.kdeconnect.Plugins.SystemVolumePlugin;
 import android.content.Context;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
+
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -40,17 +42,17 @@ public class SystemVolumePlugin extends Plugin {
     }
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_systemvolume);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_systemvolume_desc);
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         if (np.has("sinkList")) {
             sinks.clear();
@@ -128,12 +130,12 @@ public class SystemVolumePlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{PACKET_TYPE_SYSTEMVOLUME};
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{PACKET_TYPE_SYSTEMVOLUME_REQUEST};
     }
 

src/org/kde/kdeconnect/Plugins/TelephonyPlugin/TelephonyPlugin.java

@@ -22,6 +22,7 @@ import android.telephony.TelephonyManager;
 import android.text.TextUtils;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 
 import org.apache.commons.lang3.ArrayUtils;
@@ -122,12 +123,12 @@ public class TelephonyPlugin extends Plugin {
     };
 
     @Override
-    public String getDisplayName() {
+    public @NonNull String getDisplayName() {
         return context.getResources().getString(R.string.pref_plugin_telephony);
     }
 
     @Override
-    public String getDescription() {
+    public @NonNull String getDescription() {
         return context.getResources().getString(R.string.pref_plugin_telephony_desc);
     }
 
@@ -263,7 +264,7 @@ public class TelephonyPlugin extends Plugin {
     }
 
     @Override
-    public boolean onPacketReceived(NetworkPacket np) {
+    public boolean onPacketReceived(@NonNull NetworkPacket np) {
 
         switch (np.getType()) {
             case PACKET_TYPE_TELEPHONY_REQUEST:
@@ -291,7 +292,7 @@ public class TelephonyPlugin extends Plugin {
     }
 
     @Override
-    public String[] getSupportedPacketTypes() {
+    public @NonNull String[] getSupportedPacketTypes() {
         return new String[]{
                 PACKET_TYPE_TELEPHONY_REQUEST,
                 PACKET_TYPE_TELEPHONY_REQUEST_MUTE,
@@ -299,14 +300,14 @@ public class TelephonyPlugin extends Plugin {
     }
 
     @Override
-    public String[] getOutgoingPacketTypes() {
+    public @NonNull String[] getOutgoingPacketTypes() {
         return new String[]{
                 PACKET_TYPE_TELEPHONY
         };
     }
 
     @Override
-    public String[] getRequiredPermissions() {
+    public @NonNull String[] getRequiredPermissions() {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
             return new String[]{
                     Manifest.permission.READ_PHONE_STATE,
@@ -318,7 +319,7 @@ public class TelephonyPlugin extends Plugin {
     }
 
     @Override
-    public String[] getOptionalPermissions() {
+    public @NonNull String[] getOptionalPermissions() {
         return new String[]{
                 Manifest.permission.READ_CONTACTS,
         };

src/org/kde/kdeconnect/UserInterface/DeviceFragment.kt

@@ -297,13 +297,13 @@ class DeviceFragment : Fragment() {
                                 device.pluginsWithoutPermissions,
                                 R.string.plugins_need_permission
                             ) { p: Plugin ->
-                                p.permissionExplanationDialog?.show(childFragmentManager, null)
+                                p.permissionExplanationDialog.show(childFragmentManager, null)
                             }
                             createPermissionsList(
                                 device.pluginsWithoutOptionalPermissions,
                                 R.string.plugins_need_optional_permission
                             ) { p: Plugin ->
-                                p.optionalPermissionExplanationDialog?.show(childFragmentManager, null)
+                                p.optionalPermissionExplanationDialog.show(childFragmentManager, null)
                             }
 
                             requireDeviceBinding().permissionsList.adapter =