Saving a civireport causes the report to crash with `TypeError: Cannot access offset of type string on string in HTML_QuickForm_advmultiselect->toHtml`
- Edit some settings on a civireport.
- Save the civireport.
- TypeError: Cannot access offset of type string on string in HTML_QuickForm_advmultiselect->toHtml() (line 807 of ...\sites\all\modules\civicrm\packages\HTML\QuickForm\advmultiselect.php).
There is no stacktrace so I'm not sure yet what it doesn't like.