How do I check if an item is in the player's hand, and that item has a value inside of it?

So basically, I'm making a GUI that will display how much ammo is left in your gun. I'm using two IntValues inside of the gun, "Ammo" and "MaxAmmo".

When I test to see if the GUI is visible or not, I get the error "Players.JoshGamingHQ1.PlayerGui.AmmoScreen.Frame.TextLabel.LocalScript:1: attempt to index a nil value".

This is the code:

local toolWithAmmo = game.Players.LocalPlayer.Character:FindFirstChildWhichIsA("Tool").Ammo
local toolWithMaxAmmo = game.Players.LocalPlayer.Character:FindFirstChildWhichIsA("Tool").MaxAmmo

local function update()

    script.Parent.Text = toolWithAmmo.Value.." / "..toolWithMaxAmmo.Value

end

while true do
    wait()
    if toolWithAmmo ~= nil and toolWithMaxAmmo ~= nil then
        script.Parent.Visible = true
        update()
    else
        script.Parent.Visible = false

    end
end

This script is a Local Script inside of a TextLabel.

(The issue may be obvious and I don't see it, I'm fairly new to Roblox Lua scripting.)