public RayGroup ReadGroup(string groupname, RayGroupList listToAdd)
 {
     if (_source != null)
     {
         return _source.ReadGroup(groupname, listToAdd);
     }
     else
     {
         return null;
     }
 }
 public RayGroup ReadGroup(string groupname, RayGroupList listToAdd)
 {
     throw new NotImplementedException();
 }