message: Avoid calling get_default_graph() during tf.enable_eager_execution()
diff: @@ -5457,8 +5457,7 @@ def enable_eager_execution_internal(config=None,
  "tf.contrib.eager.ASYNC")
  if context.default_execution_mode == context.GRAPH_MODE:
  graph_mode_has_been_used = (
  - _default_session_stack.stack
  - or len(get_default_graph().get_operations()) > 0) # pylint: disable=g-explicit-length-test
  + _default_graph_stack._global_default_graph is not None) # pylint: disable=protected-access
  if graph_mode_has_been_used:
  raise ValueError(
  "tf.enable_eager_execution must be called at program startup.")
  