12: missing argument #2 to 'find' (string expected)?

local banned = {"anti-lag", "OS.C-REX", "vaccine", "4d being", "c-rex", "nom", "game destroyer", "firespread", "rofl", "c6ouqz", "9vssb36tj", "wildfire", "antivirus"}

local dec = game:GetDescendants()
local obje
local isit

while true do
	wait()
	for _,v in ipairs(banned) do
		for _,a in ipairs(dec) do
			wait()
			isit = v:lower()
			obje = a.Name:lower()
			if obje.find(isit) then
				print("Object: " .. a.Name .. " found, quarantining to lighting.")
				a.Parent = game.Lighting
				wait()
				print("Object " .. a.Name .. " destroyed.")
				a:Destroy()
			end
		end
	end
end

Why am i getting the error 12: missing argument #2 to 'find' (string expected)? All help is appreciated!