[D7 PHP 8.1] mb_strlen(): Passing null to parameter #1 ($string) of type string is deprecated in drupal_strlen()

Thanks for reporting this! I think this is a duplicate of: 🐛 _form_validate sends null to drupal_strlen triggering deprecation notice Needs work . We also have a test in the mentioned issue, but it needs some little work to remove the extra failures, but otherwise I think it is pretty ready.

@poker10 Thanks yeah likely a dup but note this solution will resolve other similar bugs instead of playing whack-a-mole on each instance.