What is this mouse.Target bug?

I have a simple function within a script that goes as follows:

mouse.Button2Down:connect(function()
	if on and mouse.Target:findFirstChild("Runner") then
		mouse.Target:Remove()
	end
end)

Yet every once in a while the Output tells me there was an error because mouse.Target didn't exist. I can't consistently reproduce the problem and I don't know why it happens. I even tried adding "and mouse.Target" to the if statement and I still got the error. It's like it's removing it before the if statement passes or something. Any ideas?

mouse.Target can become nil.

If you point your mouse at the sky for example, mouse.Target is nil. A very simple fix would be an if statement that checks if mouse.Target ~= nil.

--Local Script
mouse.Button2Down:connect(function()
	if mouse.Target then
		if on and mouse.Target:FindFirstChild("Runner") then
			mouse.Target:Remove()
		end
	end
end)

You could also set the mouse Target as a variable,

--Local Script
mouse.Button2Down:connect(function()
	local Target = mouse.Target
	if Target then
		if on and Target:FindFirstChild("Runner") then
			Target:Remove()
		end
	end
end)

Few More Optional Changes

You're using Remove() as opposed to Destroy(). If you're not trying to re-access, or bring back, the Target, I would suggest using the Destroy function, as it's more efficient.

Here's a link to an article about this that's really interesting and goes into much more detail about this.

Here would be the final script,

--Local Script
mouse.Button2Down:connect(function()
	local Target = mouse.Target
	if Target then
		if on and Target:FindFirstChild("Runner") then
			Target:Destroy()
		end
	end
end)

I hope I helped.

Good Luck!

If I helped, don't forget to hit the accept button!