Fix release branch

library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java

@@ -668,7 +668,6 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
 
     public MediaSourceHolder(MediaSource mediaSource) {
       this.mediaSource = mediaSource;
-      this.uid = System.identityHashCode(this);
       this.timeline = new DeferredTimeline();
       this.activeMediaPeriods = new ArrayList<>();
       this.uid = new Object();

library/core/src/main/java/com/google/android/exoplayer2/trackselection/DefaultTrackSelector.java

@@ -1173,7 +1173,7 @@ public class DefaultTrackSelector extends MappingTrackSelector {
   // MappingTrackSelector implementation.
 
   @Override
-  protected final Pair<@NullableType RendererConfiguration[], @NullableType TrackSelection[]>
+  protected final Pair<RendererConfiguration[], TrackSelection[]>
       selectTracks(
           MappedTrackInfo mappedTrackInfo,
           int[][][] rendererFormatSupports,
@@ -1181,7 +1181,7 @@ public class DefaultTrackSelector extends MappingTrackSelector {
           throws ExoPlaybackException {
     Parameters params = parametersReference.get();
     int rendererCount = mappedTrackInfo.getRendererCount();
-    @NullableType TrackSelection[] rendererTrackSelections =
+    TrackSelection[] rendererTrackSelections =
         selectAllTracks(
             mappedTrackInfo,
             rendererFormatSupports,
@@ -1404,7 +1404,7 @@ public class DefaultTrackSelector extends MappingTrackSelector {
     String selectedMimeType = null;
     if (!allowMixedMimeTypes) {
       // Select the mime type for which we have the most adaptive tracks.
-      HashSet<@NullableType String> seenMimeTypes = new HashSet<>();
+      HashSet<String> seenMimeTypes = new HashSet<>();
       int selectedMimeTypeTrackCount = 0;
       for (int i = 0; i < selectedTrackIndices.size(); i++) {
         int trackIndex = selectedTrackIndices.get(i);

library/core/src/main/java/com/google/android/exoplayer2/trackselection/MappingTrackSelector.java

@@ -383,7 +383,7 @@ public abstract class MappingTrackSelector extends TrackSelector {
             rendererFormatSupports,
             unmappedTrackGroupArray);
 
-    Pair<@NullableType RendererConfiguration[], @NullableType TrackSelection[]> result =
+    Pair<RendererConfiguration[], TrackSelection[]> result =
         selectTracks(
             mappedTrackInfo, rendererFormatSupports, rendererMixedMimeTypeAdaptationSupports);
     return new TrackSelectorResult(result.first, result.second, mappedTrackInfo);
@@ -403,7 +403,7 @@ public abstract class MappingTrackSelector extends TrackSelector {
    *     RendererCapabilities#getTrackType()} is {@link C#TRACK_TYPE_NONE}.
    * @throws ExoPlaybackException If an error occurs while selecting the tracks.
    */
-  protected abstract Pair<@NullableType RendererConfiguration[], @NullableType TrackSelection[]>
+  protected abstract Pair<RendererConfiguration[], TrackSelection[]>
       selectTracks(
           MappedTrackInfo mappedTrackInfo,
           int[][][] rendererFormatSupports,