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