i'm creating an Google Assistant action and my problem is i just want to override the Default stop intent with my own sentences so that when the user says Stop or Cancel then i would like to say something like "Thanks for using the app"
Update
This feature has been available for some time, so the below answer is obsolete.
Previous Answer
Google has indicated that this is a bug, but doesn't seem to be high on their priority list to fix. In the meantime, make sure you add other "ending" phrases such as "goodbye", "thank you", "I'm done", and other phrases that make sense for your Action.