If a site had disabled search filters via the jetpack_search_disable_widget_filters filter, then when a widget was saved, it caused an undefined index notice:

PHP Notice:  Undefined index: filter_type in .../jetpack/modules/search/class.jetpack-search-widget-filters.php on line 152

I didn't catch this before because I was testing on widgets where I had previously configured a filter.

To fix this, I added a condition to not check $new_instance['filter_type'] if widget wasn't supposed to use filters.

To test:

• On a site with a professional plan
• Checkout Jetpack master
• Set add_filter( 'jetpack_search_disable_widget_filters', '__return_true' );
• Add a new Jetpack search filters widget
• Check error log for undefined index notice
• Checkout this branch
• Add a new Jetpack search filters widget
• Ensure there is no notice