PHP Fatal error: Cannot redeclare jr_mt_query_chars()

PHP Fatal error: Cannot redeclare jr_mt_query_chars() (previously declared in \wp-content\plugins\jonradio-multiple-themes\includes\admin-validate.php:268)

This happens when switching and submitting another theme in the dropdown next to Select Theme for Site Home.

jr_mt_query_chars() is declared inside jr_mt_validate_settings() which isn’t a good practice in general as the code could become finicky. jr_mt_validate_settings() seems gets called twice somewhere, so the declaration happens twice, hence the fatal error.

A way to workaround this is by making jr_mt_query_chars() as a variable to an anonymous function:$jr_mt_query_chars = function() {}

Another thing noticed were many php warnings from input elements that had not been set. For example:
PHP Warning: Undefined array key "add_path_id" in \includes\admin-validate.php on line 114

So said code in line 114:
$url = jr_mt_sanitize_url( $input['add_path_id'] ); .
It could be tweaked like this instead:
$url = jr_mt_sanitize_url( $input['add_path_id'] ?? '' );