When flagging a topic/answer/comment should not receive "Could not send mail to notify about flagged comment" warning

STEPS TO REPRODUCE

1. Go to a forum
2. Flag a topic/ answer/ comment
3. Select the reason and enter a note under Description Field
4. Click Submit
5. Notice the Warning message. However, when a comment is deleted the e-mail is sent to that specific user.

EXPECTED RESULTS

The topic/ answer/ comment is flagged successfully and no warning message appears.

ACTUAL RESULTS

The topic/ answer/ comment is flagged, but the following warning message appears: "Could not send mail to notify about flagged comment", so the notification e-mail(s) are not sent.

Currently, to receive a notification e-mail, the Admin must go to edit mode in http://localhost:8080/xwiki/bin/edit/XWiki/XWikiPreferences then Edit Objects and under Objects of type XWiki.XWikiPreferences add an e-mail address to 'Admin email' Field.

A possible temporary workaround would be adding to the warning message of the steps described above, to fill in the 'Admin email' Field in Edit Object mode.