Lightning function giving an error?

I wrote a function that generates lightning using lookVector, etc, and when I call the function I get the following error

Workspace.Player.Right Leg.Wall2:9: bad argument #1 to 'new' (Vector3 expected, got nil)

(Line 9 in the error is line 5 in the below code) I have no idea how to rectify this. 'Wall' Is the LocalScript in which this function is contained. Here is the function just in case it is needed:

function Lightning(pos,pos2,radius,numParts,model)
	radius = 0.2
	numParts = 5
	model = game.Players.LocalPlayer.Character
	local lv = CFrame.new(pos,pos2).lookVector
	local dist = (pos-pos2).magnitude
	local dbp = dist/numParts
	local last = pos
	for i = 1,numParts do
		local p = Instance.new("Part",model)
		p.FormFactor = "Symmetric"
		p.Size = Vector3.new(1,1,1)
		p.CanCollide = false
		p.Anchored = true
		p.BrickColor = BrickColor.new("Bright red")
		local x = math.random(-100,100)/100*dbp/2
		local y = math.random(-100,100)/100*dbp/2
		local p2 = CFrame.new(pos+lv*(i*dbp),pos2+lv)*CFrame.new(x,y,0)
		local dist2 = (p2.p-last).magnitude
		local mid = (p2.p+last)/2
		local m = Instance.new("BlockMesh",p)
		m.Scale = Vector3.new(radius,radius,dist2)
		p.CFrame = CFrame.new(mid,p2.p)
		last = p2.p
		game:GetService("Debris"):AddItem(p,math.random(40,100)/1000)
	end
end

Help would be appreciated. Thanks.

You aren't calling Lightning() properly

The function expects a Vector3 for arguments #1 and #2. By the looks of things, you are only calling it as Lightning() which is incorrect as it requires arguments within the parentheses in order to satisfy the requirements in the parameters.