Output keeps saying "Humanoid is not valid member of Model"?

The output error redirects to line 2. Here is the following code:

player = game.Players.LocalPlayer
playerHumanoid = player.Character.Humanoid

function update()
    local hp = playerHumanoid.Health
    local maxhp = playerHumanoid.MaxHealth

    local health = hp / maxhp

    if health <= 0 then
        script.Parent.Bar:TweenSize(UDim2.new(0.01, 0, 1, 0), "Out", "Quad", 0.2)
        script.Parent.TextLabel.Text = "0/"..maxhp.." Health"
    end

    script.Parent.Bar:TweenSize(UDim2.new(health, 0, 1, 0), "Out", "Quad", 0.2)
    script.Parent.TextLabel.Text = math.floor(hp+0.5).."/"..maxhp.." Health"

end

update()

playerHumanoid.HealthChanged:connect(update)

I have a feeling that it has to do with the lack of code that checks if the model has or doesn't have the humanoid object, but usually it only has to do with buttons that are touched (if I am correct).