Android Volley library doesn't work for localhost request

Question

I'm sending an http request from Android Java using the Volley library to a Spring backend. The backend application should responds with a JSON string. The Tomcat server is on 192.168.1.8:8080 (or localhost on the same machine) and from browser and with the http apache library requests works fine. On android I get some strange error:

public class MainActivity extends AppCompatActivity {

private TextView textResponse;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    textResponse = findViewById(R.id.responseText);
    // Instantiate the RequestQueue.
    RequestQueue queue = Volley.newRequestQueue(this);
    String url = "http://192.168.1.8:8080/admin/getAll";
    System.out.println(url);

    // Request a string response from the provided URL.
    StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
            response -> {
                // Display the first 500 characters of the response string.
                System.out.println("Response is: " + response.substring(0,500));
                textResponse.setText(response.substring(0,50));
            },
            error -> {
                System.out.println("That didn't work!" );
                textResponse.setText("error");
            });

    // Add the request to the RequestQueue.
    queue.add(stringRequest);
    //queue.start();
    System.out.println("sto qua");

}}

It goes in the error case, and if I try to get the error status code with error.networkResponse.statusCode it gives me:

Attempt to read from field 'int com.android.volley.NetworkResponse.statusCode' on a null 
object reference

Where is the problem?