2D Player Can't Move

Here is my code:

 using UnityEngine;
 using System.Collections;
 
 public class Player_Movement : MonoBehaviour 
 {
     Rigidbody2D RB2D;
     Animator Anim;
 
     // Use this for initialization
     void Start () 
     {
 
         RB2D.GetComponent<Rigidbody2D> ();
         Anim.GetComponent<Animator> ();
     }
 
     // Update is called once per frame
     void Update () 
     {
         Vector2 movement_vector = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
 
         if (movement_vector != Vector2.zero) 
         {
             Anim.SetBool ("Is Walking", true);
             Anim.SetFloat ("Input X", movement_vector.x);
             Anim.SetFloat ("Input Y", movement_vector.y);
         } else {
                     Anim.SetBool ("Is Walking", false);
                 }
 
         RB2D.MovePosition (RB2D.position + movement_vector * Time.deltaTime);
     }
 }

Unity Version: 5.3.2f1

My player won't move when I press UP, DOWN, LEFT, RIGHT arrows and getting this error.

NullReferenceException: Object reference not set to an instance of an object Player_Movement.Start () (at Assets/Scripts/Player_Movement.cs:13)

NullReferenceException: Object reference not set to an instance of an object Player_Movement.Update () (at Assets/Scripts/Player_Movement.cs:28)