Bulk editing custom links forces choice of button class

[jeremystretch]

NetBox version

v3.1.7

Python version

3.8

Steps to Reproduce

1. Create one or more custom links
2. Attempt to edit one or more custom links using the bulk edit feature without changing the button class of each

Expected Behavior

It should be possible to edit other attributes of the selected custom links without forcing the user to specify a button class.

Observed Behavior

The button class must have a choice selected, and defaults to "Default."

[jeremystretch]

A similar condition exists for the Webhook http_method and JournalEntry kind fields.