how to make a clicking cool down when you click the sky ?

A few hours ago i've made a pistol script (keep in mind that for the pistol script i used mouse.Target) but i met a error along the way in which i can't figure out a solution, so basically a pistol has a cool down, right ? it won't just shoot out bullets like a rifle so i made a cool down IF the mouse.Target is either terrain or a player, but what about the sky, the sky is equal to nil, how do i add a cool down if my mouse is pointing at the sky ? (debounce just messes up the script)

local handle = script.Parent.Handle
local tool = script.Parent
local player = game.Players.LocalPlayer
local gui = player:WaitForChild("PlayerGui")
local screenGui = gui:WaitForChild("ScreenGui")
local TextLabel = screenGui:WaitForChild("Ammo")
local mouse = player:GetMouse()
local mxAm = 10
local Ammo1 = mxAm
local serivce = game:GetService("UserInputService")
local oldIcon = mouse.Icon

local function ammo2()
	Ammo1 = mxAm
end

tool.Equipped:Connect(function()
	mouse.Icon = "http://www.roblox.com/asset/?id=79658449"
	TextLabel.Visible = true	
end)

tool.Activated:Connect(function()
	if tool.Enabled == true then
		if Ammo1 > 0 then
			Ammo1 = Ammo1 - 1
			if mouse.Target.Parent:FindFirstChild("Humanoid") then
				script.Parent.Damage:FireServer(mouse.Target)
				tool.Enabled = false
				print("target hit")
				wait(0.2)
				tool.Enabled = true
			else 
				tool.Enabled = false
				print("miss")
				wait(0.2)
				tool.Enabled = true
			end	
		end		
	end
end)	

while wait() do
	TextLabel.Text = Ammo1.."/"..mxAm

tool.Unequipped:Connect(function()
	mouse.Icon = oldIcon
	TextLabel.Visible = false
end)

serivce.InputBegan:Connect(function(key)
	if key.KeyCode == Enum.KeyCode.R and Ammo1 ~= mxAm then
		wait(1)
		ammo2()
		end
	end)
end

Here's a script with the cooldown applied, I also rewrote it for you.

if not game:IsLoaded() then
	repeat
		wait()
	until game:IsLoaded()
end

local Players = game:GetService("Players")
local UserInputService = game:GetService("UserInputService")
local RunService = game:GetService("RunService")

local LocalPlayer = Players.LocalPlayer
local Character = LocalPlayer.Character
local PlayerGui = LocalPlayer:FindFirstChildOfClass("PlayerGui")
local Mouse = LocalPlayer:GetMouse()

local ScreenGui = PlayerGui:FindFirstChildOfClass("ScreenGui")
local TextLabel = ScreenGui:FindFirstChild("Ammo")


local Tool = (script.Parent:IsA("Tool") and script.Parent) or script:FindFirstAncestorOfClass("Tool")
local Handle = Tool:FindFirstChild("Handle")

local MaxAmmo = 10
local OldMouseIcon = Mouse.Icon
local Bind = nil
local CooldownProgression = false

Tool.Equipped:Connect(function()
	Mouse.Icon = ("http://www.roblox.com/asset/?id=79658449");
	TextLabel.Visible = true
	Bind = Tool.Activated:Connect(function()
		if not Tool.Enabled or Ammo1 <= 0 or CooldownProgression == true then
			return
		end
		CooldownProgression = true
		Ammo1 = Ammo1 - 1
		local S = pcall(function()
			local TargetModel = (Mouse.Target:IsA("Model") and Mouse.Target) or (Mouse.Target.Parent:IsA("Model") and Mouse.Target.Parent) or Mouse.Target:FindFirstAncestorOfClass("Model")
			local TargetHumanoid = TargetModel:FindFirstChildOfClass("Humanoid")
			Tool.Enabled = false
			print("Target hit");
			wait(.2)
			Tool.Enabled = true
		end)
		if not S then
			Tool.Enabled = true
			print("Missed");
			wait(.2)
			Tool.Enabled = false
		end
		coroutine.wrap(function()
			wait(.25) -- Cooldown time.
			CooldownProgression = false
		end)()
	end)
	Tool.Unequipped:Wait(function()
		Bind:Disconnect()
	end)
end)

Tool.Unequipped:Connect(function()
	if Bind ~= nil and typeof(Bind) == "RBXScriptConnection" then
		Bind:Disconnect()
	end
	Mouse.Icon = OldMouseIcon
	TextLabel.Visible = false
	return
end)

UserInputService.InputBegan:Connect(function(InputObject,GameProcessedEvent)
	if GameProcessedEvent then
		return
	end
	if InputObject.KeyCode == Enum.KeyCode.R and Ammo1 ~= MaxAmmo then
		CooldownProgression = true -- Make this true so you can't fire while reloading...
		print("Reloading...")
		wait(1)
		Ammo1 = MaxAmmo
		print("Reloaded!")
		CooldownProgression = false -- Reloading complete, allow the user to fire.
	end
end)

coroutine.resume(coroutine.create(function()
	while true do
		RunService.Stepped:Wait()
		TextLabel.text = tostring(Ammo1) .. (" / ") .. tostring(MaxAmmo)
	end
end))