Michał Janiszewski 9d333bc95a Compare to None using identity is operator
This is a trivial change that replaces `==` operator with `is` operator, following PEP 8 guideline:

> Comparisons to singletons like None should always be done with is or is not, never the equality operators.

https://legacy.python.org/dev/peps/pep-0008/#programming-recommendations
2018-10-31 12:21:01 +11:00
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