Check if there are mobs alive

[tonibm19]

something like this

function OnTick()
	local LoopEntitys = function( Entity )
		if Entity:IsMob() then
			if Entity:GetUniqueID() == "Something" --something here to check if it is the right mob.
				some code here to do stuff
			end
		end
	end
end

But, I want to check if there isn't any mob and then execute the code I want. I think this code is for check if there is any mob, and if there is at least one, execute some code.