message: Add a workaround for reference cycles created by newer versions of astor.
diff: @@ -67,6 +67,12 @@ def ast_to_source(node, indentation=' '):
  trimmed_code_lines.append(l)
  code = '\n'.join(trimmed_code_lines)
  + # Work around the reference cycle generated by astor.
  + # See https://github.com/berkerpeksag/astor/blob/55dd323f7d8d696610c703c0296763c567685c31/astor/code_gen.py#L162 # pylint:disable=line-too-long
  + # Reference cycles are quite disliked by TensorFlow's tests.
  + if hasattr(generator, 'write'):
  + generator.write = None
  +
  return code
  