List Group error

Problem/Motivation

bunthorne reported:

But after this reset, I am getting php errors in the log:
Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in template_preprocess_views_bootstrap_list_group() (line 245 of /[path]/web/modules/contrib/views_bootstrap/views_bootstrap.theme.inc)

Steps to reproduce

With 5.5.0-alpha1, create a view with a style of list group. Then upgrade to 5.5.0-beta1. Without saving, see error when row class is null.

Proposed resolution

Use core process for getting row class and update to attributes.

Remaining tasks

User interface changes

API changes

Data model changes