Fix email confirmation errors in Airbrake

Fixes: https://sharetribe.airbrake.io/projects/15448/groups/69400103

Preconditions: A community with 1) email confirmation enabled and 2) allows only certain email addresses

Steps to reproduce:
1. Log out
2. Sign up for a new account
3. You should now see a email confirmation page
4. Log out
5. Go to your mailbox and click confirmation link

Expected result:
Email is confirmed, user is redirected to login page

Actual
User sees error (id for Nil class)