I get this error

[PufferFishDev]

UnassignedReferenceException: The variable m_GroundCheck of CharacterController2D has not been assigned.
You probably need to assign the m_GroundCheck variable of the CharacterController2D script in the inspector.
UnityEngine.Transform.get_position () (at <53407686a67f4d21a4ef710a7828900a>:0)
CharacterController2D.FixedUpdate () (at Assets/Scripts/CharacterController2D.cs:51)

[PandaDevX]

In the inspector tab of charactercontroller2d script in unity you need to assign the m_GroundCheck