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I have the below class. When the readJson method is called, I am getting null pointer exception in Android 6.0. How do I fix the NPE? It is working fine on most of the devices and versions, but it seems to be failing on Android 6.0. I have searched for answers, but I couldn't find the problem in the code.Im getting NPE when trying to access variables of Screens.

public class UserRepository 

 private static UserRepository instance = null;
 final String TAG = UserRepository.class.getName();
 public Resorts resortsData;
 public AppSettings appSettingsData;

 @Inject
 public Resources resources;

 public static synchronized UserRepository getInstance()
 if (instance == null)
 instance = new UserRepository();
 
 return instance;
 

 public void readJson()

 FirebaseDatabase database = FirebaseDatabase.getInstance();
 String lang = Locale.getDefault().getLanguage();
 DatabaseReference myRef = database.getReference(lang);

 myRef.addValueEventListener(new ValueEventListener() 
 @Override
 public void onDataChange(DataSnapshot dataSnapshot) 
 // This method is called once with the initial value and again
 // whenever data at this location is updated.
 resortsData = dataSnapshot.getValue(Resorts.class);
 boolean hasChild = dataSnapshot.hasChild("appSettings");
 if (hasChild)
 DataSnapshot appSettings = dataSnapshot.child("appSettings");
 appSettingsData = appSettings.getValue(AppSettings.class);
 Log.e("NAG",appSettingsData.screens.toString());
 


 //Resorts resortsData = resort.getValue(Resorts.class);
 

 @Override
 public void onCancelled(DatabaseError error) 
 // Failed to read value
 Log.w(TAG, "Failed to read value.", error.toException());
 
 );

 


public class AppSettings 
 public ArrayList<ApiEndpoints> apiEndpoints;
 public Screens screens;
 public GlobalStrings globalStrings;


public class Screens 
 public RegisterStay registerStay;
 public CalendarScreen calendar;
 public RegisterError registerError;
 public BookingNumber bookingNumber;
 public InDestDashboard inDestDashboard;
 public PreDestDashboard preDestDashboard;
 public LocalExcursions localExcursions;
 public PreDestMenu preDestMenu;
 public InDestMenu inDestMenu;
 public EmailSubscribe emailSubscribe;
 public UnregisteredLanding unregisteredLanding;

Error message

Caused by java.lang.NullPointerException: Attempt to read from field 'com.royalton.mobileapp.common.repositories.models.appSettings.screens.Screens com.royalton.mobileapp.common.repositories.models.appSettings.AppSettings.screens' on a null object reference
 at com.royalton.mobileapp.base.AppModule.providesEmailSubscribeScreen(AppModule.java:192)
 at com.royalton.mobileapp.base.AppModule_ProvidesEmailSubscribeScreenFactory.get(AppModule_ProvidesEmailSubscribeScreenFactory.java:19)
 at com.royalton.mobileapp.base.AppModule_ProvidesEmailSubscribeScreenFactory.get(AppModule_ProvidesEmailSubscribeScreenFactory.java:8)