【Unity】NullReferenceException: Object reference not set to an instance of an object の解決方を教えてください。

Error
NullReferenceException: Object reference not set to an instance of an object
TarodevController.PlayerController.OnEnable () (at Assets/Scripts/Player/PlayerController.cs:52)

が出て実行できません。

エラーが出るコード

C#
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.InputSystem;

namespace TarodevController {
    public class PlayerController : MonoBehaviour, IPlayerController {
        // Public for external hooks
        public Vector3 Velocity { get; private set; }
        public FrameInput Input { get; private set; }
        public bool JumpingThisFrame { get; private set; }
        public bool LandingThisFrame { get; private set; }
        public Vector3 RawMovement { get; private set; }
        public bool Grounded => _colDown;

        private Vector3 _lastPosition;
        private float _currentHorizontalSpeed, _currentVerticalSpeed;

        private PlayerInput input;
        private bool jump;
        private Vector2 movement;

        // This is horrible, but for some reason colliders are not fully established when update starts...
        private bool _active;
        void Awake() => Invoke(nameof(Activate), 0.5f);
        void Activate() =>  _active = true;

        void Start()
        {
            input = GetComponent<PlayerInput>();
        }

        private void Update() {
            if(!_active) return;
            // Calculate velocity
            Velocity = (transform.position - _lastPosition) / Time.deltaTime;
            _lastPosition = transform.position;

            GatherInput();
            RunCollisionChecks();

            CalculateWalk(); // Horizontal movement
            CalculateJumpApex(); // Affects fall speed, so calculate before gravity
            CalculateGravity(); // Vertical movement
            CalculateJump(); // Possibly overrides vertical

            MoveCharacter(); // Actually perform the axis movement
        }
/////////////////////////////////////////////////////////////////////////////////////////////////////////
    void OnEnable()
    {
        input.actions["Move"].performed += OnMove;
        input.actions["Move"].canceled += OnMove;

        input.actions["Jump"].performed += OnJump;
        input.actions["Jump"].canceled += OnJump;
    }
/////////////////////////////////////////////////////////////////////////////////////////////////////////
    void OnDisable()
    {
        input.actions["Move"].performed -= OnMoveStop;
        input.actions["Move"].canceled -= OnMoveStop;

        input.actions["Jump"].performed -= OnJump;
        input.actions["Jump"].canceled -= OnJump;
    }

    private void OnJump(InputAction.CallbackContext obj)
    {
        switch(obj.phase)
        {
            case InputActionPhase.Performed:
                jump = true;
                break;
            case InputActionPhase.Canceled:
                jump = false;
                break;
        }
    }

    private void OnMove(InputAction.CallbackContext obj)
    {
        movement = obj.ReadValue<Vector2>();
    }

    private void OnMoveStop(InputAction.CallbackContext obj)
    {
        movement = Vector2.zero;
    }

        #region Gather Input

        private void GatherInput() {
            Input = new FrameInput {
                JumpDown = jump, JumpUp = jump, X = movement.x
            };
            if (Input.JumpDown) {
                _lastJumpPressed = Time.time;
            }
        }

        #endregion

        #region Collisions

        [Header("COLLISION")] [SerializeField] private Bounds _characterBounds;
        [SerializeField] private LayerMask _groundLayer;
        [SerializeField] private int _detectorCount = 3;
        [SerializeField] private float _detectionRayLength = 0.1f;
        [SerializeField] [Range(0.1f, 0.3f)] private float _rayBuffer = 0.1f; // Prevents side detectors hitting the ground

        private RayRange _raysUp, _raysRight, _raysDown, _raysLeft;
        private bool _colUp, _colRight, _colDown, _colLeft;

        private float _timeLeftGrounded;

        // We use these raycast checks for pre-collision information
        private void RunCollisionChecks() {
            // Generate ray ranges. 
            CalculateRayRanged();

            // Ground
            LandingThisFrame = false;
            var groundedCheck = RunDetection(_raysDown);
            if (_colDown && !groundedCheck) _timeLeftGrounded = Time.time; // Only trigger when first leaving
            else if (!_colDown && groundedCheck) {
                _coyoteUsable = true; // Only trigger when first touching
                LandingThisFrame = true;
            }

            _colDown = groundedCheck;

            // The rest
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
　　　　　　　　　　　　　　　　　　　　　　　　　　省略
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

                positionToMoveTo = posToTry;
            }
        }

        #endregion
    }
}