code: private void reportFailedCheckpoint(Exception cause) {
  		// to prevent null-pointers from concurrent modification, copy reference onto stack
  		final PendingCheckpointStats statsCallback = this.statsCallback;
  		if (statsCallback != null) {
  			long failureTimestamp = System.currentTimeMillis();
  			statsCallback.reportFailedCheckpoint(failureTimestamp, cause);
  		}
  	}
docs: Reports a failed checkpoint with the given optional cause.
  
  @param cause The failure cause or <code>null</code>.