Failing test: yapftests.pytree_unwrapper_test.MatchBracketsTest

[FRidh]

The following test fails with Python 2.7. It does not fail with 3.6.

FAIL: testFunctionDef (yapftests.pytree_unwrapper_test.MatchBracketsTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/build/yapf-0.19.0/yapftests/pytree_unwrapper_test.py", line 325, in testFunctionDef
    [],
  File "/build/yapf-0.19.0/yapftests/pytree_unwrapper_test.py", line 314, in _CheckMatchingBrackets
    self.assertEqual(uwline[open_bracket][0], uwline[close_bracket][1])
AssertionError: FormatToken(name=LPAR, value=() != None

Log of 0.17.0: https://nix-cache.s3.amazonaws.com/log/6jbvyly8xjgqzjdf9sbvba068cvd0hp7-python2.7-yapf-0.17.0.drv
It also fails with 0.19.0.