fix: change null to None for python

[deepankarm]

Thanks for the awesome work with auto-swagger. I found an issue with null in swagger.py, replaced null with None & tested locally. Quite new to TS world, so apologies about not adding tests.

Another suggestion is, instead of writing swaggerPythonString to ./swagger/swagger.py, we should just serialize swaggerStr as a json into a file and do json.load(...) in the handler defined in swagger-json.py (This will take of handling booleans, nulls & other fields).

[bfaulk96]

Another suggestion is, instead of writing swaggerPythonString to ./swagger/swagger.py, we should just serialize swaggerStr as a json into a file and do json.load(...) in the handler defined in swagger-json.py (This will take of handling booleans, nulls & other fields).

I like this suggestion a ton more than what we're currently doing for Python.
I'll look into implementing it.