message: shape_tuple in array_ops.stack
diff: @@ -935,9 +935,9 @@ def stack(values, axis=0, name="stack"):
  except (TypeError, ValueError):
  pass # Input list contains non-constant tensors
  - value_shape = ops.convert_to_tensor(values[0], name=name).get_shape()
  - if value_shape.ndims is not None:
  - expanded_num_dims = value_shape.ndims + 1
  + value_shape = ops.convert_to_tensor(values[0], name=name)._shape_tuple() # pylint: disable=protected-access
  + if value_shape is not None:
  + expanded_num_dims = len(value_shape) + 1
  if axis < -expanded_num_dims or axis >= expanded_num_dims:
  raise ValueError("axis = %d not in [%d, %d)" % (axis, -expanded_num_dims,
  expanded_num_dims))
  