Check whether group moderates any branch while removing

Right now if we remove a user group and it appeared that this group moderating some branch (is set as moderatingGroup within some branch), then an exception is raised.
Expected result:
if a group is moderating some branches, then a message box should be shown with message: This group is set as moderating group for branches: Branch1, Branch2. In order to remove the group, you should first set another moderating group for these branches or remove them.