Adds smart json support for WTForms. Useful for when using WTForms with RESTful APIs.
WTForms added a new kwarg to `Field.process` called [extra_filters](https://github.com/wtforms/wtforms/blob/22e2cf97c65ed38911543d247ccb0fc2207e0da3/src/wtforms/fields/core.py#L318). That causes an error when using a form: `TypeError: process() got an unexpected keyword argument 'extra_filters'` This PR fixes the error, and allows for any future unknown kwargs that WTForms might add to `Field.process`.
This issue appears to be discussing a feature request or bug report related to the repository. Based on the content, it seems to be resolved. The issue was opened by alanhamlett and has received 2 comments.