Hi Joshua,
At least one issue with the code is the If condition xlist == Null. It will remain unevaluated unless xlist is Null. So the If will remain unevaluated.
{0, 1, 2, 3, 4, 5} == Null
(* {0, 1, 2, 3, 4, 5} == Null *)
If[{0, 1, 2, 3, 4, 5} == Null, True, False]
(* If[{0, 1, 2, 3, 4, 5} == Null, True, False] *)
Rather than testing for Null, test the Length of the list.
