userName is 'null' when selecting 'Invite other Users'

[lfzawacki]

To reproduce:

1. Open the modal
2. Select 'Invite other users'
3. Use the link to join with another user
4. The username will be 'null'

I understand the user has no name, but 'null' make it look like something has gone wrong. Maybe we could have a customizable name field that starts out as 'Guest'. Also, would it make sense to join users as guests in the meeting?