i got this error , attempt to index nil with 'Parent', how to fix it ? [SOLVED]

so i make a gun script, if mouse.target.parent is a humanoid, it will take a damage but i got an error

Players.BlackBooks.Backpack.Gun.MainScript:30: attempt to index nil with 'Parent'

this is the script

script.Parent.Activated:Connect(function()
        track = tool.Parent.Humanoid:LoadAnimation(anim)
        track.Priority = Enum.AnimationPriority.Action
        track.Looped = false
        if ammo > 0 and not reload and not deb then
            deb = true
            ammo = ammo - 1
            script.Parent.FireSound:Play()
            track:Play()
            if mouse.Target.Parent:FindFirstChild("Humanoid") then -- this is line 30
                if mouse.Target.Parent.Name ~= player.Name then
                    script.Parent.DealDamage:FireServer(mouse.Target.Parent, 20)
                end
            end
            wait(0.5)
            deb = false
        elseif reload == false and ammo == 0 then
            reloads()
        end
        while wait() do
            text.Text = ammo.." / "..maxAmmo
        end
    end)

and this is the full script, just so you can see it clearly

local maxAmmo = 10
local ammo = maxAmmo
local reload = false
local player = game.Players.LocalPlayer
local gui = player:WaitForChild("PlayerGui")
local text = gui:WaitForChild("Ammo"):FindFirstChild("Ammo")
local deb = false
local tool = script.Parent
local anim = Instance.new("Animation")
anim.AnimationId = "rbxassetid://5992010544"
local track

script.Parent.Equipped:Connect(function(mouse)
    local function reloads()
        reload = true
        script.Parent.Reload:Play()
        wait(1.5)
        ammo = maxAmmo
        reload = false
    end
    script.Parent.Activated:Connect(function()
        track = tool.Parent.Humanoid:LoadAnimation(anim)
        track.Priority = Enum.AnimationPriority.Action
        track.Looped = false
        if ammo > 0 and not reload and not deb then
            deb = true
            ammo = ammo - 1
            script.Parent.FireSound:Play()
            track:Play()
            if mouse.Target.Parent:FindFirstChild("Humanoid") then -- this line is error
                if mouse.Target.Parent.Name ~= player.Name then
                    script.Parent.DealDamage:FireServer(mouse.Target.Parent, 20)
                end
            end
            wait(0.5)
            deb = false
        elseif reload == false and ammo == 0 then
            reloads()
        end
        while wait() do
            text.Text = ammo.." / "..maxAmmo
        end
    end)
    local input = game:GetService("UserInputService")
    input.InputBegan:Connect(function(key)
        if key.KeyCode == Enum.KeyCode.R and reload == false and ammo ~= maxAmmo then
            reloads()
        end
    end)
end)

i appreciate every helpers. Thanks for replying