You can absolutely check an empty array’s length. However, if you try to do that on a null reference you’ll get an exception. I suspect that’s what you’re running into. You can cope with both though:
if (array == null || array.Length == 0)
If that isn’t the cause, please give a short but complete program demonstrating the problem. If that was the cause, it’s worth taking a moment to make sure you understand null references vs “empty” collections/strings/whatever.