forbid register with handles='index' and datamask='all'
we cannot allow @register(handles='index', datamask='all' because in this case all data will be masked but never unmasked again. this is certainly seldom what the user want.
we cannot allow @register(handles='index', datamask='all' because in this case all data will be masked but never unmasked again. this is certainly seldom what the user want.