[issue28649] refleak in typing.py

[Ivan Levkivskyi]

Ivan Levkivskyi added the comment:

A very simple repro:

    with self.assertRaises(TypeError):
        Union[[]]

It looks like the problem happens when a non-hashable argument is passed to cached function

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28649>
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