message: Make the noop returned by tpu.replicate() trigger TPU computations.
diff: @@ -623,6 +623,11 @@ def split_compile_and_replicate(computation,
  vscope.set_use_resource(saved_use_resource)
  + # If the computation returns `None`, add `no_op` here so that when user
  + # fetches `no_op` returned by this function, the TPUExecute node will be
  + # triggered.
  + if outputs is None:
  + outputs = (control_flow_ops.no_op(),)
  # If the computation only returned one value, makes it a tuple.
  if not isinstance(outputs, (list, tuple)):
  outputs = (outputs,)
  