Group Picker Custom Field is being populated with brackets for the default group set, hence it isn't sending notifications

Steps to reproduce:
1. Add a Custom Field with type 'Group Picker' to a project and associate to an
issue type. Add to issue default issue screen.
2. Set the default value to any user group.
3. Set Notification to be sent to the user group when issue is created.
4. Go to Agile - Planning Board and add this custom field to the Card view.
5. Now click on New Card
6. The default group that appears in the custom field is enclosed within
square brackets. Because of this square brackets, the mail notification is
not sent our to the members of the group. If you remove the square brackets
and then add the new card then the mail gets sent out.
7. Note, this issue is not seen when you add an issue from the issue detail
screen.