Can't change group notification email when periods are in the name

Summary

I can't change my notification email for a specific group because GitLab returns a HTTP 500 error page.

Steps to reproduce

1. Be part of at least one group
2. Visit https://gitlab.com/profile/notifications
3. In the "Groups" section, click on the dropdown list on the right of the row for a group
4. Select an email

What is the current bug behavior?

https://gitlab.com/profile/notifications/groups/GROUP_NAME opens up with an HTTP 500 error page

What is the expected correct behavior?

The selected email should become the notification email for the selected group

Relevant logs and/or screenshots

Annotazione_2019-09-05_140543

Output of checks

This bug happens on GitLab.com