Fix NullPointerException in queue handling

app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java

@@ -1728,18 +1728,27 @@ public class VideoDetailFragment
     @Override
     public void onQueueUpdate(final PlayQueue queue) {
         playQueue = queue;
+        if (DEBUG) {
+            Log.d(TAG, "onQueueUpdate() called with: serviceId = ["
+                    + serviceId + "], videoUrl = [" + url + "], name = ["
+                    + name + "], playQueue = [" + playQueue + "]");
+        }
+
         // This should be the only place where we push data to stack.
         // It will allow to have live instance of PlayQueue with actual information about
         // deleted/added items inside Channel/Playlist queue and makes possible to have
         // a history of played items
-        if ((stack.isEmpty() || !stack.peek().getPlayQueue().equals(queue)
+        @Nullable final StackItem stackPeek = stack.peek();
-                && queue.getItem() != null)) {
+        if (stackPeek != null && stackPeek.getPlayQueue().equals(queue)) {
-            stack.push(new StackItem(queue.getItem().getServiceId(),
+            @Nullable final PlayQueueItem playQueueItem = queue.getItem();
-                    queue.getItem().getUrl(),
+            if (playQueueItem != null) {
-                    queue.getItem().getTitle(),
+                stack.push(new StackItem(playQueueItem.getServiceId(), playQueueItem.getUrl(),
-                    queue));
+                        playQueueItem.getTitle(), queue));
-        } else {
+                return;
-            final StackItem stackWithQueue = findQueueInStack(queue);
+            } // else continue below
+        }
+
+        @Nullable final StackItem stackWithQueue = findQueueInStack(queue);
         if (stackWithQueue != null) {
             // On every MainPlayer service's destroy() playQueue gets disposed and
             // no longer able to track progress. That's why we update our cached disposed
@@ -1749,13 +1758,6 @@ public class VideoDetailFragment
         }
     }
 
-        if (DEBUG) {
-            Log.d(TAG, "onQueueUpdate() called with: serviceId = ["
-                    + serviceId + "], videoUrl = [" + url + "], name = ["
-                    + name + "], playQueue = [" + playQueue + "]");
-        }
-    }
-
     @Override
     public void onPlaybackUpdate(final int state,
                                  final int repeatMode,
@@ -2055,6 +2057,7 @@ public class VideoDetailFragment
         return url == null;
     }
 
+    @Nullable
     private StackItem findQueueInStack(final PlayQueue queue) {
         StackItem item = null;
         final Iterator<StackItem> iterator = stack.descendingIterator();

app/src/main/java/org/schabi/newpipe/player/playqueue/PlayQueue.java

@@ -167,19 +167,20 @@ public abstract class PlayQueue implements Serializable {
     }
 
     /**
-     * @return the current item that should be played
+     * @return the current item that should be played, or null if the queue is empty
      */
+    @Nullable
     public PlayQueueItem getItem() {
         return getItem(getIndex());
     }
 
     /**
      * @param index the index of the item to return
-     * @return the item at the given index
+     * @return the item at the given index, or null if the index is out of bounds
-     * @throws IndexOutOfBoundsException
      */
+    @Nullable
     public PlayQueueItem getItem(final int index) {
-        if (index < 0 || index >= streams.size() || streams.get(index) == null) {
+        if (index < 0 || index >= streams.size()) {
             return null;
         }
         return streams.get(index);