This door is not in use conumdrum

Door.cs

public class Door {
    public Door(bool closed, bool hasNotInUseSign) {
        this.InUse = closed;
        this.HasNotInUseSign = hasNotInUseSign;
    }

    public State State => this.GetState();

    private State GetState() {
        if (InUse && !HasNotInUseSign) {
            return InUseAndFunctional;
        }

        if (InUse && HasNotInUseSign) {
            return InUseAndNotFunctional;
        }

        if (!InUse && !HasNotInUseSign) {
            return NotInUseAndFunctional;
        }

        if (!InUse && HasNotInUseSign) {
            return NotInUseAndNotFunctional;
        }
    }

    public void CloseDoor()
    {
        this.InUse = true;
    }
    
    public void OpenDoor()
    {
        this.InUse = false;
    }

    public void AddNotInUseSign()
    {
        this.HasNotInUseSign = true;
    }

    public void RemoveNotInUseSign()
    {
        this.HasNotInUseSign = false;
    }

    public bool InUse { get; private set; }

    public bool HasNotInUseSign { get; private set; }

    public enum State {
        InUseAndFunctional,
        InUseAndNotFunctional,
        NotInUseAndFunctional,
        NotInUseAndNotFunctional
    }
}