Fix possible dashboard warning #18829

Hello
I am using matomo 4.7.1 , it is working fine and tracking the events but I am getting this warning sometimes
This is the request I am sending through postman:
http://localhost/matomo/piwik.php?idsite=22&rec=1&e_c=inbox&e_a=archiveMessage&uid=961000&dimension1=1&dimension2=1&dimension3=1

@mkassir95 I guess I found the issue. It might occur while archiving if you tracked a custom dimension for an action without an url. created a PR to fix that.

Thank you