@Override
    public void operationComplete(ChannelFuture future) throws Exception {
      Throwable cause = future.cause() == null ? exception : future.cause();
      if (cause != null) {
        handleChannelWriteFailure(cause, false);
      } else {
        cleanupChunks(null);
      }
      logger.debug("Chunk cleanup complete on channel {}", ctx.channel());
    }
Instantiate a CleanupCallback with an exception to return once cleanup is activated.
@param exception the {@link Exception} to return as a part of the callback. Can be {@code null}. This can be
                 overriden if the channel write ended in failure.
ambry-rest/src/main/java/com/github/ambry/rest/NettyResponseChannel.java