Error attempting to index a nil value?

The script is suppose to allow the player to simulate "shooting" and when there cursor goes over a player, they will take damage. the issue is, after a while of "shooting" i get this error attempt to index local 'raw' (a nil value)

Any solutions?

player = game.Players.LocalPlayer
character = player.Character
gun = character:FindFirstChild("Rifle")
mouse = player:GetMouse()
auto = false
function getModel(raw)
    for _, child in pairs(workspace:GetChildren()) do
    --calling pairs is barely any slower than using next directly, plus it's easier to read.
        if raw:IsDescendantOf(child) then
            return child;
        end;
    end;
    return nil; --this allows us to not use pcall
end;

mouse.Button1Down:connect(function()
	wait()
    auto = true
    while auto do
	wait()
    if mouse.Target then
	wait()
        local model = getModel(mouse.Target)
        if model and model:FindFirstChild("Humanoid") then
	wait()
            model.Humanoid.Health = model.Humanoid.Health - 15
            wait(0.2)
			game.ReplicatedStorage.gun.Value = game.ReplicatedStorage.gun.Value - 1
    end
mouse.Button1Up:connect(function()
    auto = false
end)
        end
    end
end)

Well, as seen in your question, you're indexing a nil value. The only thing I can think of making game.Players.LocalPlayer:GetMouse().Target return nil is this script's implementation.

This script should be ran from a LocalScript, since LocalScripts are the only class that can invoke game.Players.LocalPlayer and have it work correctly throughout servers.

Hope this helps! Comment if you need more assistance or a further explanation!