private Set<UserGroup> redefineGroups() {
   Set<UserGroup> userGroups = new HashSet<UserGroup>(userToUpdate.getGroups());
   for (String newGroup : groupDefinitions.getSource()) {
     UserGroup userGroup = registrationDao.findGroupByGroupName(newGroup);
     userGroups.remove(userGroup);
   }
   for (String newGroup : groupDefinitions.getTarget()) {
     UserGroup userGroup = registrationDao.findGroupByGroupName(newGroup);
     userGroups.add(userGroup);
   }
   return userGroups;
 }