How can I fix this error?

NullReferenceException: Object reference not set to an instance of an object PlayerMovement.Move () (at Assets/Scripts/PlayerMovement.cs:17)

The console send me +999 messages of this error when the game starts

using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
public Joystick joystickMove;
public Rigidbody rb;
public float speed;
public float fuerzaSalto;

private void Start()
{

}

void Move()
{
    rb.velocity = new Vector3(joystickMove.Horizontal * speed, rb.velocity.y, joystickMove.Vertical * speed);
}

public void JumpBt()
{
    rb.velocity += Vector3.up * fuerzaSalto;
}

private void Update()
{
    Move(); 
}

}

This is all my code

If someone prefers to write me on discord i will send it to you

Thank you so much

private Rigidbody rb;

    private void Awake()
   {
        rb = GetComponent<Rigidbody>();
   }

Always make variables and methods private unless being accessed from outside the class, and then use properties to access them.

public Rigidbody rb Have you assigned the rigidbody component in Inspector?