Vector3 Expected; got nil?

Working on a GUI when I stumbled on an error with vector3's. An error on line 8

local function GenerateSelectionModel()
	if SelectionModel then
		SelectionModel:Destroy()
	end
	local Prefab = PrefabTable[SelectionNumber]
	if Prefab then
		SelectionModel = Prefab:Clone()
		SelectionModel:SetPrimaryPartCFrame(CFrame.new(Mouse.Hit.p) * CFrame.Angles(0, math.rad(CurrentRotation), 0) * CFrame.new(SelectionModel:FindFirstChild("Compensation")) or {Value = Vector3.new() * CFrame.new(0, SelectionModel.PrimaryPart.Size.Y / 2, 0)})
		local Cache = SelectionModel:GetDescendants()
		Mouse.TargetFilter = SelectionModel
		for i = 1, #Cache do
			if Cache[i]:IsA("BasePart") then
				Cache[i].Material = Enum.Material.Glass
				if Cache[i]:IsA("UnionOperation") then
					Cache[i].UsePartColor = true
				end
				if Cache[i]:IsA("Seat") then
					Cache[i].Disabled = true
				end
				if Cache[i].Transparency ~= 1 then
					Cache[i].Transparency = 0.5
				end
				Cache[i].CanCollide = false
			end
		end
		if Equipped then
			SelectionModel.Parent = PrefabsFolder
		end
	end
end

This is a local script inside StarterCharacterScripts; if you need more information do ask. Thanks