ServerScriptService.BulletCreate:18: attempt to index nil with 'PlayerGui'?

ServerScriptService.BulletCreate:18: attempt to index nil with 'PlayerGui' ^ That's the error.

I'm trying to make a gun when it hits someones head, it shows a text saying 'HEADSHOT!'

This is my code, a normal script.

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local remoteEvent = ReplicatedStorage:WaitForChild("Shot")
local ShotBullet = false
remoteEvent.OnServerEvent:Connect(function(player, gunPos, mosPos)


    local Bullet = Instance.new("Part")
    Bullet.Name = "Bullet"
    Bullet.Parent = game.Workspace
    Bullet.BrickColor = BrickColor.new("Really black")
    Bullet.Size = Vector3.new(0.28, 0.29, 0.25)
    Bullet.Touched:Connect(function(hit)
        if hit.Parent:FindFirstChild("Humanoid") then
            hit.Parent.Humanoid.Health = hit.Parent.Humanoid.Health - 5
            Bullet:Destroy()
            if hit.Parent:FindFirstChild("Head") then
                hit.Parent.Humanoid.Health = hit.Parent.Humanoid.Health - 10
                game.Players.LocalPlayer.PlayerGui.ScreenGui.Headshot.Visible = true
                wait(2)
                game.Players.LocalPlayer.PlayerGui.ScreenGui.Headshot.Visible = false
            end
        end
        end)


    local bulletspeed = 300
    Bullet.CFrame = CFrame.new(gunPos, mosPos)
    Bullet.Velocity = Bullet.CFrame.lookVector * bulletspeed

wait(1)
        Bullet:Destroy()

    end)