Unexpected default salt in 2.0.0 where I used to pass None as a salt in 1.1.0 about itsdangerous

[davidism]

I didn't think using None just to replace it with a string made sense, typically the "default None" pattern is used for mutable or complex defaults. I also didn't expect users to be passing None, either they would not pass it and get the serializer's default b"itsdangerous", or they would pass it explicitly and get that value for namespace purposes.

Since it can affect the validity of tokens, I'll make a bugfix release. However, I'd recommend you set an explicit default regardless, as it makes more sense to set a default namespace that is related to your own project.