What does this output mean? Weld Parent Error

I made this script:

function sit(child)
	if child.Name == "SeatWeld" then
		character = child.Part1.Parent
		if player.Value ~= character.Name then -- check if the player is the one I want
			child:Destroy()
		end
	end
end
script.Parent.ChildAdded:connect(sit)

It's supposed to destroy the seatweld when an undesired player sits, but when I tried to seat there, it didn't work and the output said this: Something unexpectedly tried to set the parent of SeatWeld to NULL while trying to set the parent of SeatWeld. Current parent is Seat. What is wrong? I didn't try to change it's parent, so why that error?