Currently having an issue with a gun I'm making, can anybody help me?

I'm currently making a game, and can't seem to figure out what is wrong with my script. The only thing showing up in output is something about line 26, but it isn't an error. Does anybody know to make it so it actually attaches to the camera instead of staying on the floor?

Here is the script:

repeat
	wait()
until game:IsLoaded()

local plr = game.Players.LocalPlayer
local char = plr.Character
local mouse = plr:GetMouse()
local cam = workspace.CurrentCamera

local Run = game:GetService("RunService")

local RS = game.ReplicatedStorage
local GunModules = RS:WaitForChild("GunModules")
local GunModels = RS:WaitForChild("GunModels")

local Primary = "Assault Rifle"
local WeaponInHand
local WeaponData

local maincf = CFrame.new() --weapon offset of camera

plr.CameraMode = Enum.CameraMode.LockFirstPerson

Run.RenderStepped:Connect(function()
	if WeaponInHand then
		WeaponInHand:SetPrimaryPartCframe(
			cam.CFrame
			* maincf
		)
	end
	
end)

function setup(weapon)
	WeaponData = require(GunModules:WaitForChild("Assault Rifle"))
	
	maincf = WeaponData.MainCFrame
	
	WeaponInHand = GunModels:WaitForChild(weapon)
	WeaponInHand.PrimaryPart = WeaponInHand:WaitForChild("Handle")
	WeaponInHand.Parent = cam
	for i, part in pairs(WeaponInHand:GetChildren()) do
		if part:IsA("BasePart") then
			part.Anchored = true
			part.CanColide = false
		end
	end
end

setup(Primary)