Error with Exception in thread "main" java.lang.NullPointerException [duplicated]

Hi, I would like to see if you could help me see what the error really is I do not understand it:

Exception in thread "main" java.lang.NullPointerException
    at formulariomedico.Vista.<init>(Vista.java:89)
    at formulariomedico.Formulariomedico.main(Formulariomedico.java:9)
C:\Users\nic21\AppData\Local\NetBeans\Cache.2\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 2 seconds)

and in other cases, it does not have a main method (re-creating it in a new project). main:     package formulariomedico;

public class Formulariomedico {

    public static void main(String[] args) {

        Vista v = new Vista();
    }    
}

the view I want to create:

package formulariomedico;
import java.awt.*;
import javax.swing.*;
public class Vista extends JFrame {

 JLabel titulo, nom, nom2, ape, ape2, doc, numdoc, direc, tel, cor, ciu, sex, dep, zona;
 JTextField tnom, tnom2, tape, tape2, tdoc, tdirec, ttel, tcor, tciud, tdep;
 JComboBox menuaño, menudias, menumes, tipodoc, sexo, czona;
 JButton guardar;
 String mes[] = {
  "Enero",
  "Febrero",
  "Marzo",
  "Abril",
  "Mayo",
  "Junio",
  "Julio",
  "Agosto",
  "Septiembre",
  "Octubre",
  "Noviembre",
  "Diciembre"
 };
 String docu[] = {
  "TI",
  "CC",
  "CE",
  "DNI"
 };
 String se[] = {
  "Hombre",
  "Mujer"
 };
 String zon[] = {
  "Urbana",
  "Rural"
 };
 Vista() {
  setTitle("Formulario de inscripción titulo");
  setLayout(null);
  setSize(550, 650);
  titulo = new JLabel("titulo");
  titulo.setForeground(Color.BLUE);
  nom = new JLabel("Primer Nombres: ");
  nom2 = new JLabel("Segundo nombre: ");
  ape = new JLabel("Primer Apellido: ");
  ape2 = new JLabel("Segundo Apellido: ");
  doc = new JLabel("Tipo de documento: ");
  numdoc = new JLabel("Numero de documento: ");
  sex = new JLabel("Sexo: ");
  tel = new JLabel("Telefono: ");
  cor = new JLabel("Correo: ");
  direc = new JLabel("Dirección: ");
  ciu = new JLabel("Lugar de Residencia: ");
  dep = new JLabel("Departamento: ");
  zona = new JLabel("Zona: ");

  tnom = new JTextField();
  tnom2 = new JTextField();
  tape = new JTextField();
  tape2 = new JTextField();
  tdoc = new JTextField();
  tdirec = new JTextField();
  tciud = new JTextField();
  tdep = new JTextField();

  menuaño = new JComboBox();
  for (int i = 1920; i <= 2018; i++) {
   menuaño.addItem("" + i);
  }
  menudias = new JComboBox();
  for (int i = 1; i <= 31; i++) {
   menudias.addItem("" + i);
  }
  menumes = new JComboBox(mes);
  tipodoc = new JComboBox(docu);
  sexo = new JComboBox(se);
  czona = new JComboBox(zon);

  guardar = new JButton("Guardar");
  guardar.setBounds(200, 680, 150, 30);

  titulo.setBounds(10, 10, 200, 30);
  nom.setBounds(10, 50, 200, 30);
  nom2.setBounds(10, 90, 200, 30);
  ape.setBounds(10, 130, 200, 30);
  ape2.setBounds(10, 170, 200, 30);
  doc.setBounds(10, 210, 200, 30);
  numdoc.setBounds(10, 240, 200, 30);
  direc.setBounds(10, 280, 200, 30);
  tel.setBounds(10, 320, 200, 30);
  cor.setBounds(10, 360, 200, 30);
  ciu.setBounds(10, 400, 200, 30);
  sex.setBounds(10, 440, 200, 30);
  dep.setBounds(10, 480, 200, 30);
  zona.setBounds(10, 520, 200, 30);

  tnom.setBounds(210, 50, 200, 30);
  tnom2.setBounds(210, 90, 200, 30);
  tape.setBounds(210, 130, 200, 30);
  tape2.setBounds(210, 170, 200, 30);
  tipodoc.setBounds(210, 210, 200, 30);
  tdoc.setBounds(210, 240, 200, 30);
  tdirec.setBounds(210, 270, 200, 30);
  ttel.setBounds(210, 300, 200, 30);
  tcor.setBounds(210, 330, 200, 30);
  tciud.setBounds(210, 360, 200, 30);
  sexo.setBounds(210, 400, 200, 30);
  tdep.setBounds(210, 440, 200, 30);

  this.add(titulo); //agregarlo al frame
  this.add(nom);
  this.add(nom2);
  this.add(ape);
  this.add(ape2);
  this.add(doc);
  this.add(numdoc);
  this.add(direc);
  this.add(tel);
  this.add(cor);
  this.add(ciu);
  this.add(sex);
  this.add(dep);
  this.add(zona);


  this.add(tnom);
  this.add(tnom2);
  this.add(tape);
  this.add(tape2);
  this.add(tdoc);
  this.add(tdirec);
  this.add(ttel);
  this.add(tcor);
  this.add(tciud);
  this.add(tdep);
  this.add(menuaño);
  this.add(menudias);
  this.add(menumes);
  this.add(tipodoc);
  this.add(sex);
  this.add(czona);
  this.add(guardar);

  setVisible(true);
  setDefaultCloseOperation(3);

 }


}