public static EventGroupFilter Apply(Filter filter)
            {
                EventGroupFilter result;

                if (filter != null)
                {
                    var finder = new DoConvert();
                    filter.AcceptVisitor(finder);

                    result = finder.lastResult_;
                }
                else
                {
                    result = null;
                }

                return(result);
            }
 public static EventGroupFilter Convert(Filter filter)
 => DoConvert.Apply(filter) ?? MatchAll.Instance;