No default value set for tabindex causing errors in server logs

Hi,

The settings indicate that if no tabindex is set a default value of 0 is used, yet the following errors are shown by WP_DEBUG running on PHP 7.3.8, WP 5.2.3, Collapse-O-Matic, 1.7.11:
Notice: Undefined index: tabindex in ../plugins/jquery-collapse-o-matic/collapse-o-matic.php on line 875

Perhaps checking if the key is present in the saved_options array and assigning 0 if not would silence the errors:
if($key == ‘tabindex’ ) {
$this->options[ $key ] = in_array( $key, $saved_options ) ? $saved_options[ $key ] : 0; }

While it’s only a PHP Notice, a resolution would be appreciated without the user having to explicitly state the setting.
Thank you,
Connect.