Mouse.Hit.p problem? [CFrame]

ERROR :

"Attempt to call a nil value"

I want my "Head" to cframe to my mouse (Like daxter33's head rotation)

Where you move your mouse your head stays on your character, but it will rotate to your mouse.

function SetHeadPos(Pos)
if not Pos then return end
local run,error = ypcall(function()
    local Weld = Instance.new("Weld")
    Weld.Part0 = Char.Torso
    Weld.Part1 = Char["Head"]
    Weld.C0 = CFrame.new(0, 1.4, 0)
    Weld.Parent = Weld.Part0

    pcall(function()
        for _,v in pairs(Char.Head:GetChildren()) do
            if v.ClassName=='SpecialMesh' then
                v:remove()
            end
        end
    end)

    if Char:findFirstChild('Head') then
        pcall(function()
            for _,v in pairs(Char:GetChildren()) do
                if v.ClassName == 'Hat' then
                    v:remove()
                end
            end
            local jointPosition = Weld.Part0.CFrame:toWorldSpace(CFrame.new(1, 0.5, 0))
            local cframe = CFrame.new(jointPosition.p, Pos) * CFrame.Angles(math.pi/2, 0, 0) * CFrame.new(0, -1, 0)
            Weld.C0 = Weld.Part0.CFrame:toObjectSpace(cframe)
        end)
    end
end)
if not run then end
end

Run.Heartbeat:connect(SetHeadPos(Plr:GetMouse().Hit.p))