Debug message on the screen

Hi.

While I was testing your plugin, after clearing transients, I received this message in the screen (my debug is active):

Undefined index: clean_optimize in D:\Var\www\html\wp-content\plugins\artiss-transient-cleaner\includes\clean-transients.php on line 148

https://ww.wp.xz.cn/plugins/artiss-transient-cleaner/