None gets listed as if it was part of a enum

[GideonKoenig]

Describe the bug

In some parameter Type definitions, none gets listed as part of a enum. It doesn't actually get included in it, so the example provided would be parsed into a enum with two types (SQTR and LOG2).

To Reproduce

sklearn.ensemble.ExtraTreesClassifier.__init__.max_features

Type says:
{"sqrt", "log2", None}, int or float, default="sqrt"

Expected behavior

None should be listed as it's own type:
{"sqrt", "log2", None}, int or float, default="sqrt"
-> {"sqrt", "log2"}, int or float or None, default="sqrt"
or not at all
-> {"sqrt", "log2"}, int or float, default="sqrt"

Screenshots (optional)

No response

Additional Context (optional)

No response