On second thought, this might cause Lua errors for people who call this manually since this existed for so long.
Looking through the global GitHub instances, I can't find any where people manually call SWEP.Precache -- it used to be called automatically, anyway. Also, even if they manually called it, they must have overrided it right? Or else they'd be calling an empty method.
I guess we shall see. SWEP.Precache was never automatically called, the hook is a myth and never actually existed.