NullReferenceExpection: Object reference not set to an instance of an object error.

Hello. So i have been working on my script for movement for my character and untill recently, it was working just fine. here is the full error: NullReferenceException: Object reference not set to an instance of an object PlayerMovement.FixedUpdate () (at Assets/Character/Scripts/PlayerMovement.cs:32)

Does anyone have any ideas on whats going on? Here is the script:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerMovement : MonoBehaviour {
 
     public float speed = 6f;
     Vector3 movement;
     Rigidbody playerrigidbody;
     bool IsFlying = false;
     public float mousesensetivity = 2f;
 
     void Start () {
 
         playerrigidbody = GetComponent<Rigidbody>();
   
     
     }
     
     // Update is called once per frame
     void FixedUpdate () {
         // rotation
         float h = Input.GetAxisRaw("Horizontal");
         float v = Input.GetAxisRaw("Vertical");
         move(h, v);
 
         float Xrot = Input.GetAxisRaw("Mouse X") * mousesensetivity;
         transform.Rotate (0, Xrot, 0);
 
         float Yrot = Input.GetAxisRaw("Mouse Y") * mousesensetivity;
 
         Camera.main.transform.Rotate(Yrot, 0, 0);
 
        Vector3 speed = new Vector3(h, 0, v);
 
        speed = transform.rotation * speed;
 
     }
 
     void move (float h, float v)
     {
         if (Input.GetKey(KeyCode.Space))
         {
             if (IsFlying == false)
             {
                 IsFlying = true;
                 GetComponent<Rigidbody>().velocity = new Vector3(0, 6, 0);
 
             }
         }
         Vector3 Speed = new Vector3(h, 0, v);
 
         Speed = transform.rotation * Speed / 6;
 
 
         movement.Set(h, 0f, v);
 
         playerrigidbody.MovePosition(transform.position + Speed);
     }
 
     void OnCollisionEnter(Collision col)
     {
         if (col.gameObject.name == "floor" || col.gameObject.name == "PlatformPrototype08x01x08" || col.gameObject.name == "StepsPrototype04x02x02" || col.gameObject.name == "PlatformPrototype02x01x02")
         {
             IsFlying = false;
         }
     }
 
 }