Form widget Ajax failing with mb_strtolower warning

Problem/Motivation

Using php 8.2 and trying to modify the entity browser widgets setting gets an Ajax parse error due to an "mb_strtolower(): Passing null to parameter is deprecated" warning embedded in the returned content.

Steps to reproduce

Convert an existing site to php 8.2 and try to change settings.

Proposed resolution

This is related to the core bug 🐛 Querying with NULL values results in warning mb_strtolower(): Passing null to parameter is deprecated Needs work which seems to be stalled.

Problem is that the bundle type can be null. Solution is to convert null bundles to "" which bypasses the core bug.

Remaining tasks

See attached patch.