R1:1720209f16c3

Various PHP 8.1 strlen(null) fixes for Dashboard Panels

Summary:
In the dashboard application (https://my.phorge.site/dashboard/), when creating panels, adding panels to tab panels, and viewing query panels, we get a variety of strlen(null) errors under PHP 8.1.

This fixes all the ones seen.

Fixes T15574

Test Plan: See T15574

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: avivey, speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest…