Unable to create extra field on user entity

I am able to create a view based field in the UI, but when I try to import the field definition from config/install/ in a custom module, I get that same TypeError.

Thanks for the work on this, I was able to review and made minor changes/additions to this feature. It's now apart of the 2.x dev branch and will be merge in the coming days if no issues have been reported.

Thanks!

Just adding a note for others who may have used this patch prior to merging:

The changes made prior to merging will break your site - I can't clear caches after applying the new version. I'm currently figuring out how to address the issue and will edit the post when I have a solution.

Automatically closed - issue fixed for 2 weeks with no activity.