@Override
  @Nullable
  public synchronized ByteBuffer getByteBuffer() {
    Preconditions.checkNotNull(mBufRef);
    return mBufRef.get().getByteBuffer();
  }
Gets the size of the ByteBuffer if it is valid. Otherwise, an exception is raised

@return the size of the ByteBuffer if it is not closed.
@throws {@link ClosedException}
imagepipeline/src/main/java/com/facebook/imagepipeline/memory/MemoryPooledByteBuffer.java