Fix some PHP 7.4 array index access issues
Summary: Ref T13518. See https://discourse.phabricator-community.org/t/more-exceptions-when-viewing-diffs/3789/. Under PHP 7.4, accessing an array index of values like false and null is no longer valid. This is great, but we occasionally do it.
- Upgraded to PHP 7.4.
- Loaded revisions with added/changed lines, inlines, and Asana support configured.
- Before patch: saw various fatals around accessing indexes of booleans and nulls.
- After patch: clean revision.
Maniphest Tasks: T13518
Differential Revision: https://secure.phabricator.com/D21172