Blank emails affects the group sharing functionality

If you have a user without a email added into a group and try to share a page with that group the notification will show as "Sent" in the sharing work box, however the emails will not be send to any of the group's member.

Confluence does not allow blank emails when users are added, however if you add those users trough a user directory (AD/LDAP) you will be able to reproduce the scenario of this bug

Steps to reproduce.

1. Set up a AD/LDAP.
2. Add the following users as per bellow image in AD/LDAP:
   
   In above scenario I added a valid email on admin user and Bruce Banner user.
3. Create a user directory to synchronize those users.
4. Setup a mail server in Confluence.
5. Create the following groups:
   • test1
   • test2
   • test3
6. In "test1" add the following users:
   • aarons
   • admin
   • bbanner
7. In "test2" add the following users:
   • admin
   • aevans
   • bbanner
8. In "test3" add the following users:
   • admin
   • bbanner
9. Create a blank Page.
10. Share the page with test3 group.
    This group have emails added into all it's members.
11. Note that you will get a notification, which is expected.
12. Now share with test1 group.
    The first member does not have a email added.
13. You will get a sent confirmation in the workbox.
14. Notice that your valid accounts will not get the emails as they got with test3 group.
15. There are no errors in the logs and neither in the Confluence mail queues.
16. If you use test2 group, which have the first user with a valid email and the second user with a blank email, you will get a notification to the "admin" user but not for "bbanner".

Workaround

If you remove the users that have blank emails from the target group and share it again, it will work as expected.