[docs] [issue27183] Clarify that Py_VISIT(NULL) does nothing

[Roundup Robot]

Roundup Robot added the comment:

New changeset 7c67cb3b54b4 by Benjamin Peterson in branch '3.5':
note that Py_VISIT handles NULL (closes #27183)
https://hg.python.org/cpython/rev/7c67cb3b54b4

New changeset 42356e44af23 by Benjamin Peterson in branch '2.7':
note that Py_VISIT handles NULL (closes #27183)
https://hg.python.org/cpython/rev/42356e44af23

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nosy: +python-dev
resolution:  -> fixed
stage:  -> resolved
status: open -> closed

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27183>
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