@RequiresSession
  public AlertGroupEntity findGroupById(long groupId) {
    return entityManagerProvider.get().find(AlertGroupEntity.class, groupId);
  }
Gets an alert group with the specified ID.

@param groupId
         the ID of the group to retrieve.
@return the group or {@code null} if none exists.
ambari-server/src/main/java/org/apache/ambari/server/orm/dao/AlertDispatchDAO.java