Android MVVM And Retrofit Api Response Is Null

This function is used to Login the user. I am using data binding and RxJava

public void loginUser(String idNumber, String password) {
    RetrofitService.getApiService()
            .agentLogin(new LoginRequest(idNumber, password))
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Action1<Response<LoginResponse>>() {
                @Override
                public void call(Response<LoginResponse> userResponse) {
                    if (userResponse.isSuccessful() ) {
                        executor.execute(new Runnable() {
                            @Override
                            public void run() {

                                Log.i("AUTHKEY",userResponse.body().getUser().getAuthKey());
                                userDao.insert(userResponse.body().getUser());
                            }
                        });
                    }
                }
            });

}

The app fails when I log Log.i("AUTHKEY",userResponse.body().getUser().getAuthKey());

Error java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Integer com.vuna.agent.model.LoginResponse$User.getId()' on a null object reference

From the Okhttp logger, the server returns the right response

2019-04-12 12:33:36.707 28896-29064/com.vuna.agent D/OkHttp: <-- 200 OK http://example.com/login (923ms)

2019-04-12 12:33:36.709 28896-29064/com.vuna.agent D/OkHttp: {"code":201,"message":"You are now logged in!","id":2,"firstname":"Victor","lastname":"Amwollo","authkey":"22sA1JvVo4hmzhps1NVIO7_B6f4yCp_e"}
2019-04-12 12:33:36.709 28896-29064/com.vuna.agent D/OkHttp: <-- END HTTP (141-byte body)

Here is the LoginResponse class with an inner Entity class

public class LoginResponse {

    private Boolean success;

    private User user;


    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }


    @Entity(tableName = "user")
    public static class User {

        @PrimaryKey(autoGenerate = true)
        @SerializedName("id")
        private Integer id;

        private String firstName;
        private String lastName;

        private String authKey;

        //getters and setters

    }
}

Why am I getting the error?

You get the null pointer because your json does not map to LoginResponse.

try

public class LoginResponse {

    private Boolean success;
    private Integer id;
    private String firstName;
    private String lastName;
    private String authKey;

}

I cleaned up your RX. Note: Brackets might be wrong as I am used to kotlin.

public void loginUser(String idNumber, String password) {
    RetrofitService.getApiService()
        .agentLogin(new LoginRequest(idNumber, password))
        .filter { it.isSuccessful(); }
        .map { it.body(); }
        .map { new User(it.getId()...) /* covert LoginResponse to User here */ } 
        .flatMapCompletable { Completable.fromAction { userDao.insert(it); } }
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe();                                 
}