[最佳答案] You would typically get that if code uses .First() or .Single() on a sequence (IEnumerable<T>) that has (as the message suggests): no elements. Meaning: an empty sequence (not to be confused with a null sequence). You don't show code that does that, so I can only assume this happens inside .GetLatLongFromAddress(). So it sounds like there is a bug, probably relating to the "not found" case, but in code that we can't see. Personally, I would expect the "not found" case