public RegionItemModel(ZActivityOperations activityOperations, string controllerAction, string masterEntity = null, string masterKey = null, RegionViewModel region = null)
     : this()
 {
     ActivityOperations = activityOperations;
     ControllerAction   = controllerAction;
     MasterEntity       = masterEntity;
     MasterKey          = masterKey;
     Region             = region ?? Region;
 }