E/Volley: [40176] NetworkDispatcher.processRequest: Unhandled exception java.lang.NullPointerException

Question

I am sending information from my android application to my database by php, however when I execute it and with a spinner I select some of the available options and I give it the following results, I tried to fix it but always says that, I dont know what to do, please help!

2020-06-30 08:50:48.688 19172-19330/com.example.tallerof E/Volley: [40176] NetworkDispatcher.processRequest: Unhandled exception java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference

Here the class where I put everything to send it to php

 package com.example.tallerof;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import java.util.HashMap;
import java.util.Map;

public class Aceptado extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

    String valor;
    String rol;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_aceptado);
        Spinner snipper= findViewById(R.id.spi);
        Button ir= findViewById(R.id.button10);
        ArrayAdapter<CharSequence> adapter= ArrayAdapter.createFromResource(this, R.array.Estatus, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        snipper.setAdapter(adapter);
        snipper.setOnItemSelectedListener(this);
        valor = getIntent().getStringExtra("matricula");
        ir.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                servicio("https://tallerof.000webhostapp.com/Actualiza.php");

            }
        });
    }


    private void servicio(String URL){

        StringRequest stringRequest= new StringRequest(Request.Method.POST, URL, new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                Toast.makeText(getApplicationContext(), "Listo", Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(Aceptado.this, MainActivity2.class);
                startActivity(intent);

            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(getApplicationContext(),error.toString(),Toast.LENGTH_SHORT).show();
            }
        }) {
            @Override
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String,String> parametros= new HashMap<String,String>();
                parametros.put("Id_nuevo",rol);
                parametros.put("Aceptado","1");
                parametros.put("Matricula_Nuevo",valor);


                return parametros;
            }
        };
        RequestQueue requestQueue= Volley.newRequestQueue(this);
        requestQueue.add(stringRequest);

    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        String text= parent.getItemAtPosition(position).toString();
        if(text.equals("Alumno")){
            rol="1";
        }
        if(text.equals("Maestro")){
            rol="2";
        }
        if(text.equals("Administracion")){
            rol="3";
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {

    }
}

Answer 1

The problem was that I was passing variables incorrectly with the intent