Hammer.Skill:71: attempt to perform arithmetic (sub) on number and nil?

I keep getting this error and the damage isnt working how do i fix this?

if hit.Parent:FindFirstChild("Humanoid")then
			if hit.Parent.Name ~= plr.Name then
				if DB == false then
					DB = true
					print(SlashDamage)
					wait()
					hit.Parent.Humanoid.Health  = hit.Parent.Humanoid.Health - SlashDamage
					wait(0.5)
					DB = false
				end
			end
		end
	end)