why Does My Script telling that it attempted to index nil with "GetMouse()"?

So i am making a gun (I made 1 post about it) that when your clicking on the player It Will take damage.

heres the script:

wait(3)
local mouse = game.Players.LocalPlayer:GetMouse() -- Cant get mouse
local Handle = script.Parent.Handle
local Gun = script.Parent
local ShootSound = script.Parent.Handle.Shoot
local Humanoid = game.Players.LocalPlayer.Character.Humanoid
Gun.Activated:Connect(function()
	mouse.Button1Down:Connect(function()
		if mouse.target.Parent:FindFirstChild("Humanoid").Parent ~=  game.Players.LocalPlayer.Name then
			Humanoid:TakeDamage(20)
			ShootSound:Play()
		else
			ShootSound:Play()	
		end
	end)
end)

Now The problem Is That It says it cant index nil with getmouse() Is there any way i can fix it?

thanks

/HKprogram

hm.. well... first, the code should be on a local script second, try doing some waits

--Add this on the start (replace the wait(3) with this code)
wait(3)
repeat wait() until game.Players
repeat wait() until game.Players.LocalPlayer

and so that should work, if not, then try to use prints to see the problem