Fix invalid @Nullable handling in TextureBufferImpl.

Bug: None
Change-Id: Ic0b75c62512e9bcb88d562c754e4ed38058a5ece
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157886
Reviewed-by: Paulina Hensman <phensman@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29650}
diff --git a/sdk/android/api/org/webrtc/TextureBufferImpl.java b/sdk/android/api/org/webrtc/TextureBufferImpl.java
index 3d3bbab..8d75216 100644
--- a/sdk/android/api/org/webrtc/TextureBufferImpl.java
+++ b/sdk/android/api/org/webrtc/TextureBufferImpl.java
@@ -39,7 +39,7 @@
   private final Handler toI420Handler;
   private final YuvConverter yuvConverter;
   private final RefCountDelegate refCountDelegate;
-  private final @Nullable RefCountMonitor refCountMonitor;
+  private final RefCountMonitor refCountMonitor;
 
   public TextureBufferImpl(int width, int height, Type type, int id, Matrix transformMatrix,
       Handler toI420Handler, YuvConverter yuvConverter, @Nullable Runnable releaseCallback) {
@@ -53,7 +53,9 @@
 
           @Override
           public void onDestroy(TextureBufferImpl textureBuffer) {
-            releaseCallback.run();
+            if (releaseCallback != null) {
+              releaseCallback.run();
+            }
           }
         });
   }