Bug on Parser.php line 278

I get the following error:
PHP Warning: Trying to access array offset on value of type null in /var/www/html/wp-content/plugins/revision-manager-tmc/vendor/tmc/shellpress/lib/Mustache/Parser.php on line 278

Currently using:
PHP: 8.0.11
WP: 5.8.2
Revision Manager TMC: 2.7.91

Instructions to Duplicate:
Enable the Revision Manager TMC plugin
Run command wp --allow-root help then exit the help screen.

Line 278 of Parser.php:
if ($parent[Mustache_Tokenizer::TYPE] === Mustache_Tokenizer::T_PARENT) {

This seems to fix it:
if (is_array($parent) && $parent[Mustache_Tokenizer::TYPE] === Mustache_Tokenizer::T_PARENT) {