XP Command not working properly

If you add an "L" behind the ammount of XP, it will cause an error instead of adding ammout of level to the player.

Steps to reproduce:

1.  Create / open a new world with cheats ON.
2. Run the following command: /xp 10L @s

Expected Results:

• The command should gives yourself 10 levels.

Observed Results:

• The command isn't giving any level or experience to yourself, and an eror is given instead.