Undefined index: id when updating settings

When I make a change on the Settings > Performance tab to the option “Index variations”, the option changes and is saved, but there is an error recorded:

PHP Notice: Undefined index: id in \wordpress\wp-content\plugins\advanced-woo-search\includes\admin\class-aws-admin-options.php on line 101

The code appears to be looking for an index ‘id’ which is not defined in $_POSTS[$values] for the “Clear cache” section. This is what is in $_POSTS[$values]:

(
    [name] => Clear cache
    [type] => html
    [desc] => Clear cache for all search results.
    [html] => <div id="aws-clear-cache"><input class="button" type="button" value="Clear cache"><span class="loader"></span></div><br>
)