code: @Override
    public void mutate(Mutation mutation) throws IOException {
      handleExceptions();
      addCallback(helper.mutate(mutation), mutation);
    }
docs: {@inheritDoc}
  
  Being a Mutation. This method will block if either of the following are true:
  1) There are more than {@code maxInflightRpcs} RPCs in flight
  2) There are more than {@link #getWriteBufferSize()} bytes pending