NullPointerException: Attempt to invoke virtual method 'void io.realm.Realm.beginTransaction()' on a null object reference - nullpointerexception

Question

So I am making an app where I use an activity to introduce data about cities using Realm. I want to save the data when the floating action button is pressed but I keep getting a NullPointerExeption and when I debbug the app I see that realm in realm.beginTransaction() is null..
Can someone give an advice on why this happens? Thank you!
City class:
package com.android.bianca.cityworld2.models;
import com.android.bianca.cityworld2.app.MyApplication;
import io.realm.RealmObject;
import io.realm.annotations.PrimaryKey;
import io.realm.annotations.Required;
/**
* Created by Bianca on 25/01/2017.
*/
public class City extends RealmObject {
#PrimaryKey
private int id;
#Required
private String nombre;
#Required
private String description;
#Required
private String imagen;
public City(){
};
public City(String nombre, String description, String imagen) {
this.id = MyApplication.CityID.incrementAndGet();
this.nombre = nombre;
this.description = description;
this.imagen = imagen;
}
public int getID(){ return id;}
public String getNombre() {
return nombre;
}
public void setNombre(String nombre) {
this.nombre = nombre;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public String getImagen() {
return imagen;
}
public void setImagen(String imagen) {
this.imagen = imagen;
}
}
AddEditActivity:
package com.android.bianca.cityworld2.activities;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import com.android.bianca.cityworld2.R;
import com.android.bianca.cityworld2.models.City;
import com.squareup.picasso.Picasso;
import io.realm.Realm;
public class AddEditActivity extends AppCompatActivity {
private FloatingActionButton fabSave;
private Realm realm;
private TextView textViewNombre;
private TextView textViewDescription;
private ImageView imageViewImagen;
private TextView textViewUrlFoto;
private ImageView imageViewPreview;
private City ciudadNueva;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_edit);
Realm.init(getApplicationContext());
Realm realm = Realm.getDefaultInstance();
bindReferences();
imageViewPreview.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String imageURL = textViewUrlFoto.getText().toString();
if(imageURL.equals("")) {
Toast.makeText(AddEditActivity.this, "No has introducido ningun url", Toast.LENGTH_SHORT).show();
}else {
Picasso.with(AddEditActivity.this).load(imageURL).error(R.mipmap.ic_star).fit().into(imageViewImagen);
}
}
});
fabSave.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
crearNuevaCiudad();
}
});
}
private void crearNuevaCiudad(){
String nombre = textViewNombre.getText().toString().trim();
String desc = textViewDescription.getText().toString().trim();
String img = textViewUrlFoto.getText().toString().trim();
ciudadNueva = new City(nombre,desc,img);
realm.beginTransaction();
realm.copyToRealm(ciudadNueva);
realm.commitTransaction();
//<Toast.makeText(AddEditActivity.this, nombre + "|"+description+"|"+img, Toast.LENGTH_SHORT).show();
}
private void bindReferences(){
fabSave = (FloatingActionButton) findViewById(R.id.fabSave);
textViewNombre =(TextView) findViewById(R.id.editTextEditAddNombre);
textViewDescription =(TextView) findViewById(R.id.editTextAddEditDescription);
textViewUrlFoto =(TextView) findViewById(R.id.editTextEditAddUrl);
imageViewImagen = (ImageView) findViewById(R.id.imageViewEditAddBackground);
imageViewPreview = (ImageView) findViewById(R.id.imageViewEditAddPreview);
}
}
MyApplication:
package com.android.bianca.cityworld2.app;
import android.app.Application;
import com.android.bianca.cityworld2.models.City;
import java.util.concurrent.atomic.AtomicInteger;
import io.realm.Realm;
import io.realm.RealmConfiguration;
import io.realm.RealmObject;
import io.realm.RealmResults;
/**
* Created by Bianca on 26/01/2017.
*/
public class MyApplication extends Application {
public static AtomicInteger CityID = new AtomicInteger();
#Override
public void onCreate() {
setUpRealmConfig();
Realm realm = Realm.getDefaultInstance();
CityID = getIdByTable(realm, City.class);
realm.close();
}
private void setUpRealmConfig() {
Realm.init(this);
RealmConfiguration config = new RealmConfiguration.Builder().deleteRealmIfMigrationNeeded().build();
Realm.setDefaultConfiguration(config);
}
private <T extends RealmObject> AtomicInteger getIdByTable(Realm realm, Class<T> anyClass) {
RealmResults<T> results = realm.where(anyClass).findAll();
return (results.size() > 0) ? new AtomicInteger(results.max("id").intValue()) : new AtomicInteger();
}
}
Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.android.bianca.cityworld2">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".activities.MainActivity">
</activity>
<activity android:name=".activities.AddEditActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>