Problem with Health Display Script Not Sure How to Fix?

I am trying to make a health display script which seems to only work in studio but not in the actual game.

I get no errors at all in studio but in game it says "Players.Aepi.PlayerGui.StatsUI.HealthDisplay.Health.Health.Health:1: attempt to index field 'Character' (a nil value)"

To be honest i'm not sure what this error means, if someone could help that would be nice and thank you!

local Human = game.Players.LocalPlayer.Character.Humanoid

function update()
	local hpMath = Human.Health / Human.MaxHealth
	script.Parent.Size = UDim2.new(hpMath,0,1,0)
	script.Parent.Size = UDim2.new(hpMath,0,1,0)
	if Human.Health < Human.MaxHealth / 4 then
		script.Parent.BackgroundColor3 = Color3.new(255, 0, 0)
	elseif
		Human.Health > Human.MaxHealth / 4 then
		script.Parent.BackgroundColor3 = Color3.new(47/255, 255/255, 123/255)
	end
end

update()
Human.Changed:connect(update)