Please fix this Attempt to index nil error?

There is an "Attempt to index nil with Value error. Can anyone please fix it?

local Player = game.Players.LocalPlayer
local Character = Player.Character or Player.CharacterAdded:Wait()

local Humanoid = Character:WaitForChild("Humanoid")
local IsSprinting = Player:WaitForChild("IsSprinting")
local Stamina = Player:WaitForChild("Stamina")

local UserInputService = game:GetService("UserInputService")

UserInputService.InputBegan:Connect(function(Input,GameProcessed)
    if GameProcessed or Stamina == 0 then return end
    if Input.KeyCode == Enum.KeyCode.LeftShift then
        Humanoid.WalkSpeed = Character.Humanoid.WalkSpeed + 8
        IsSprinting.Value = true
    end
end)
UserInputService.InputEnded:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.LeftShift then
        Humanoid.WalkSpeed = Character.Humanoid.WalkSpeed - 8
        IsSprinting.Value = false
    end
end)

while wait() do
    if Stamina == 0 and IsSprinting.Value == true then
        IsSprinting = false
        Humanoid.WalkSpeed = 16
    end
    if IsSprinting.Value == true and Humanoid.MoveDirection.Magnitude > 0 then
        Stamina.Value = Stamina.Value - 1
        wait(1)
    else
        Stamina.Value = Stamina.Value + 1
        wait(1)
    end
    Stamina = math.clamp(Stamina.Value,0,100)
end