Why is Character Nil?

This script should be playing an animation based on the value within the script. But instead I get this error.

00:34:49.183 - Players.Player1.PlayerGui.PlayerInputManager:50: attempt to index field 'Character' (a nil value)

The script is inserted into the players gui when a guibutton is clicked. Thanks for any help.

    local player = game:GetService('Players').LocalPlayer

    local already_ran = false
    local grounded = false
    local idleAnimation = Instance.new("Animation")
    idleAnimation.AnimationId = "rbxassetid://356344446"
    local Left = Instance.new("Animation")
    Left.AnimationId = "rbxassetid://356344643"
    local Right = Instance.new("Animation")
    Right.AnimationId = "rbxassetid://326922088"
    local Forward = Instance.new("Animation")
    Forward.AnimationId = "rbxassetid://312976450"
    local Backward = Instance.new("Animation")
    Backward.AnimationId = "rbxassetid://312976450"
    local Jump = Instance.new("Animation")
    Jump.AnimationId = "rbxassetid://326922088"


    function playAnimation(parent)
        local AnimTrack = player.Character.Humanoid:LoadAnimation(parent)
        AnimTrack:Stop()
        wait(.01)
        AnimTrack:Play()
    end

    function onGround(speed)
        if grounded == false then
            grounded = true
        end
        if speed > 1  then
            if already_ran == false then
                already_ran = true
                playAnimation(Left)

            end


            elseif speed > 0 and already_ran == true  then
            already_ran = false
            playAnimation(idleAnimation)



                end
            end



    player.Character.Humanoid.Running:connect(onGround)



function onKeyPress(inputObject, gameProcessedEvent)
    if inputObject.KeyCode == Enum.KeyCode.A then
        print("Left!!")
        script.Asset.Value = ("Left")
        elseif inputObject.KeyCode == Enum.KeyCode.D then
        script.Asset.Value = ("Right")
        elseif  inputObject.KeyCode == Enum.KeyCode.W then
        script.Asset.Value = ("Forward")
        elseif  inputObject.KeyCode == Enum.KeyCode.S then
        script.Asset.Value = ("Backward")

    end
end
        game:GetService("UserInputService").InputBegan:connect(onKeyPress)