(C#) The description makes no mention of handling null values, yet "Test Empty" in the hidden test cases tests with a null value.
It's also unclear what "Text Exception" is testing, or what it's passing. It seems to expect false when my otherwise-valid solution returns true.
The only valid case in C# for an IEnumerator to throw an exception is if the underlying collection is modified during iteration. Strings are immutable so this is an unreachable scenario.