Undefined index warning post-activation

After activation, anywhere that this plugin’s code gets called (Customizer > Widgets, or Widget Options), the following warning will appear if WP_DEBUG is enabled:

Notice: Undefined index: q2w3_fixed_widget in /[domain server path]/html/wp-content/plugins/q2w3-fixed-widget/q2w3-fixed-widget.php on line 175

I’ve seen this in a few other plugins too. Once you save options and refresh the page, the warning goes away.

https://ww.wp.xz.cn/plugins/q2w3-fixed-widget/