[issue17810] Implement PEP 3154 (pickle protocol 4)

[Roundup Robot]

Roundup Robot added the comment:

New changeset d719975f4d25 by Christian Heimes in branch 'default':
Issue #17810: Add NULL check to save_frozenset
http://hg.python.org/cpython/rev/d719975f4d25

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17810>
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