private void addHandler(final Handler handler, final String type, final EntityAction... action) {
        final Map<EntityAction, List<Handler>> map = handlers.computeIfAbsent(type, k -> new HashMap<>());
        if (action == null || action.length == 0) {
            addHandlerForAction(map, handler, null);
        } else {
            for (final EntityAction act : action) {
                addHandlerForAction(map, handler, act);
            }
        }
    }
Check to see if we can find a handler for this event. If there isn't one
then there is no point in firing the event.
stroom-core/src/main/java/stroom/core/entity/event/EntityEventHandler.java