Merge pull request #96 from fengdai:release

PiperOrigin-RevId: 458883441
(cherry picked from commit 486c3504)

testutils/src/main/java/com/google/android/exoplayer2/testutil/StubPlayer.java

@@ -68,6 +68,7 @@ public class StubPlayer extends BasePlayer {
   }
   }
 
 
   @Override
   @Override
+  @Nullable
   public PlaybackException getPlayerError() {
   public PlaybackException getPlayerError() {
     throw new UnsupportedOperationException();
     throw new UnsupportedOperationException();
   }
   }