message: Fix bug preventing one from not specifying additional function attributes.
diff: @@ -529,7 +529,7 @@ class Function(object):
  self._num_outputs = len(self._func_graph.outputs)
  self._output_shapes = tuple(
  output.shape for output in self._func_graph.outputs)
  - self._attrs = _parse_func_attrs(attrs)
  + self._attrs = _parse_func_attrs(attrs or {})
  self._device_functions = tuple(
  self._func_graph._device_functions_outer_to_inner) # pylint: disable=protected-access
  