Fixed a lot of possible issues raised by a code inspection

app/src/main/java/com/cappielloantonio/play/model/Playlist.java

@@ -3,6 +3,8 @@ package com.cappielloantonio.play.model;
 import android.os.Parcel;
 import android.os.Parcelable;
 
+import androidx.annotation.NonNull;
+
 public class Playlist implements Parcelable {
     public static final String ALL = "ALL";
     public static final String DOWNLOADED = "DOWNLOADED";
@@ -66,6 +68,7 @@ public class Playlist implements Parcelable {
         return id.hashCode();
     }
 
+    @NonNull
     @Override
     public String toString() {
         return id;

app/src/main/java/com/cappielloantonio/play/service/MultiPlayer.java

@@ -133,7 +133,7 @@ public class MultiPlayer implements Playback {
         String uri = MusicUtil.getSongFileUri(song);
         MediaItem mediaItem = exoPlayer.getCurrentMediaItem();
 
-        if (mediaItem != null && mediaItem.playbackProperties.uri.toString().equals(uri)) {
+        if (mediaItem != null && mediaItem.playbackProperties != null && mediaItem.playbackProperties.uri.toString().equals(uri)) {
             return;
         }
 

app/src/main/java/com/cappielloantonio/play/ui/fragment/SettingsFragment.java

@@ -19,7 +19,6 @@ import com.cappielloantonio.play.R;
 import com.cappielloantonio.play.helper.ThemeHelper;
 import com.cappielloantonio.play.interfaces.ScanCallback;
 import com.cappielloantonio.play.ui.activity.MainActivity;
-import com.cappielloantonio.play.util.PreferenceUtil;
 import com.cappielloantonio.play.viewmodel.SettingViewModel;
 
 public class SettingsFragment extends PreferenceFragmentCompat {
@@ -36,7 +35,8 @@ public class SettingsFragment extends PreferenceFragmentCompat {
 
         someActivityResultLauncher = registerForActivityResult(
                 new ActivityResultContracts.StartActivityForResult(),
-                result -> { });
+                result -> {
+                });
     }
 
     @Override
@@ -63,19 +63,6 @@ public class SettingsFragment extends PreferenceFragmentCompat {
     public void onResume() {
         super.onResume();
 
-        findPreference("logout").setOnPreferenceClickListener(preference -> {
-            PreferenceUtil.getInstance(requireContext()).setUser(null);
-            PreferenceUtil.getInstance(requireContext()).setServer(null);
-            PreferenceUtil.getInstance(requireContext()).setPassword(null);
-            PreferenceUtil.getInstance(requireContext()).setToken(null);
-            PreferenceUtil.getInstance(requireContext()).setSalt(null);
-            PreferenceUtil.getInstance(requireContext()).setServerId(null);
-
-            activity.quit();
-
-            return true;
-        });
-
         findPreference("scan_library").setOnPreferenceClickListener(preference -> {
             settingViewModel.launchScan(new ScanCallback() {
                 @Override

app/src/main/java/com/cappielloantonio/play/ui/fragment/bottomsheetdialog/SongBottomSheetDialog.java

@@ -32,7 +32,6 @@ import com.cappielloantonio.play.viewmodel.SongBottomSheetViewModel;
 import com.google.android.material.bottomsheet.BottomSheetDialogFragment;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 

app/src/main/java/com/cappielloantonio/play/ui/fragment/dialog/PlaylistEditorDialog.java

@@ -124,7 +124,7 @@ public class PlaylistEditorDialog extends DialogFragment {
                 toPosition = target.getBindingAdapterPosition();
 
                 Collections.swap(playlistDialogSongHorizontalAdapter.getItems(), fromPosition, toPosition);
-                recyclerView.getAdapter().notifyItemMoved(fromPosition, toPosition);
+                Objects.requireNonNull(recyclerView.getAdapter()).notifyItemMoved(fromPosition, toPosition);
 
                 return false;
             }

app/src/main/java/com/cappielloantonio/play/ui/fragment/dialog/ServerSignupDialog.java

@@ -112,10 +112,10 @@ public class ServerSignupDialog extends DialogFragment {
     }
 
     private boolean validateInput() {
-        serverName = bind.serverNameTextView.getText().toString().trim();
+        serverName = Objects.requireNonNull(bind.serverNameTextView.getText()).toString().trim();
-        username = bind.usernameTextView.getText().toString().trim();
+        username = Objects.requireNonNull(bind.usernameTextView.getText()).toString().trim();
-        password = bind.passwordTextView.getText().toString();
+        password = Objects.requireNonNull(bind.passwordTextView.getText()).toString();
-        server = bind.serverTextView.getText().toString().trim();
+        server = Objects.requireNonNull(bind.serverTextView.getText()).toString().trim();
         directAccess = bind.directAccessCheckbox.isChecked();
 
         if (TextUtils.isEmpty(serverName)) {

app/src/main/java/com/cappielloantonio/play/util/MusicUtil.java

@@ -32,8 +32,8 @@ public class MusicUtil {
     }
 
     public static String getReadableDurationString(long duration, boolean millis) {
-        long minutes = 0;
+        long minutes;
-        long seconds = 0;
+        long seconds;
 
         if (millis) {
             minutes = (duration / 1000) / 60;