Notifications to null ?

[jpmurray]

I was checking the documentation, and then the comments in the config file. They all states that there's the 'mail' and 'slack' notification out of the box but...

Can one be set to null ? I couldn't see any reference for this. For example: I only wish to receive the notification on failures, so I'd only set to mail those related to errors, and send others to null.