gistfile1.txt

public static void ForSingleMaybe<T>(this IEnumerable<T> sequence, Action<T> action)
  {
		using(var enumerator = sequence.GetEnumerator())
		{
			if(!enumerator.MoveNext())
				return;
			
			var item = enumerator.Current;
			if(enumerator.MoveNext())
			     throw new InvalidOperationException("Sequence contains too many elements");
			action(item);
		}
	}