Fix invalid return of of e:weapon() (#3238)

lua/entities/gmod_wire_expression2/core/weapon.lua

@@ -14,16 +14,16 @@ __e2setcost(2) -- temporary
 
 [nodiscard]
 e2function entity entity:weapon()
-	if not IsValid(this) then return nil end
-	if not this:IsPlayer() and not this:IsNPC() then return nil end
+	if not IsValid(this) then return self:throw("Invalid entity!", NULL) end
+	if not this:IsPlayer() and not this:IsNPC() then return self:throw("Expected a Player or NPC but got Entity", NULL) end
 
 	return this:GetActiveWeapon()
 end
 
 [nodiscard]
 e2function entity entity:weapon(string weaponclassname)
-	if not IsValid(this) then return nil end
-	if not this:IsPlayer() and not this:IsNPC() then return nil end
+	if not IsValid(this) then return self:throw("Invalid entity!", NULL) end
+	if not this:IsPlayer() and not this:IsNPC() then return self:throw("Expected a Player or NPC but got Entity", NULL) end
 
 	return this:GetWeapon(weaponclassname)
 end