Revert "flake8 is wrongly suggesting to replace '== None' by 'is None'"

This reverts commit ceb4d39608fb4b4f38c62b5f8a789194f33c8959.

Goddamnit, lies!

/
| A class is free to implement comparison any way it chooses, and it can
| choose to make comparison against None mean something (which actually
| makes sense; if someone told you to implement the None object from
| scratch, how else would you get it to compare True against itself?).
\