StackOverflowError Retrofit With Basic Authentication

I have a ServiceGenerator that creates the retrofit for min, it works fine when I login and password for it, but when I try to use it without these options, my code goes into a loop and crash the app like this:

12-22 01:27:55.088 8500-8500/doupenglish.com.br.doup D/Error: ERR: stack=java.lang.StackOverflowError: stack size 8MB
at doupenglish.com.br.doup.Service.ServiceGenerator.createService(ServiceGenerator.java:29)
at doupenglish.com.br.doup.Service.ServiceGenerator.createService(ServiceGenerator.java:35)
at doupenglish.com.br.doup.Service.ServiceGenerator.createService(ServiceGenerator.java:35)
at doupenglish.com.br.doup.Service.ServiceGenerator.createService(ServiceGenerator.java:35) 
etc

My ServiceGenerator class:

package doupenglish.com.br.doup.Service;

import android.text.TextUtils;

import okhttp3.Credentials;
import okhttp3.OkHttpClient;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class ServiceGenerator {

    private static final String API_BASE_URL = "http://api.doupenglish.com.br/";

    private static OkHttpClient.Builder httpClient = new OkHttpClient.Builder();

    private static Retrofit.Builder builder =
            new Retrofit.Builder()
                    .baseUrl(API_BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create());

    private static Retrofit retrofit = builder.build();

    public static <S> S createService(Class<S> serviceClass) {
        return createService(serviceClass, null, null);
    }

    public static <S> S createService(
            Class<S> serviceClass, String username, String password) {
        if (!TextUtils.isEmpty(username)
                && !TextUtils.isEmpty(password)) {
            String authToken = Credentials.basic(username, password);
            return createService(serviceClass, authToken);
        }

        return createService(serviceClass, null, null);
    }

    public static <S> S createService(
            Class<S> serviceClass, final String authToken) {
        if (!TextUtils.isEmpty(authToken)) {
            AuthenticationInterceptor interceptor =
                    new AuthenticationInterceptor(authToken);

            if (!httpClient.interceptors().contains(interceptor)) {
                httpClient.addInterceptor(interceptor);

                builder.client(httpClient.build());
                retrofit = builder.build();
            }
        }

        return retrofit.create(serviceClass);
    }
}

Interceptor

class AuthenticationInterceptor implements Interceptor {
    private String authToken;

    public AuthenticationInterceptor(String token) {
        this.authToken = token;
    }

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request original = chain.request();

        Request.Builder builder = original.newBuilder()
                .header("Authorization", authToken);

        Request request = builder.build();
        return chain.proceed(request);
    }
}

And finally the call

    ApiInterface apidoup = ServiceGenerator.createService(ApiInterface.class);
    Call<List<NoticiaModel>> noticias = apidoup.getnoticias();
    noticias.enqueue(new Callback<List<NoticiaModel>>() {
        @Override
        public void onResponse(Call<List<NoticiaModel>> call, Response<List<NoticiaModel>> response) {
            if (response.isSuccessful()){
                //List<NoticiaModel> a = response.body();
                rv_noticas.setAdapter(new AdapterNoticias(getContext(),response.body()));
                mProgressDialog.dismiss();
            }else{
                Log.e(TAG, "onResponse: Erro API noticias " + response.code());
                mProgressDialog.dismiss();
            }
        }
        @Override
        public void onFailure(Call<List<NoticiaModel>> call, Throwable t) {
            Log.e(TAG, "onResponse: Erro API Conexao " + t);
            mProgressDialog.dismiss();

        }
    });

Resolved:

    package doupenglish.com.br.doup.Service;

import android.text.TextUtils;

import okhttp3.Credentials;
import okhttp3.OkHttpClient;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class ServiceGenerator {

    private static final String API_BASE_URL = "http://api.doupenglish.com.br";

    private static OkHttpClient.Builder httpClient = new OkHttpClient.Builder();

    private static Retrofit.Builder builder =
            new Retrofit.Builder()
                    .baseUrl(API_BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create());

    private static Retrofit retrofit = builder.build();

    public static <S> S createService(Class<S> serviceClass) {
        return createService(serviceClass, null, null);
    }

    public static <S> S createService( Class<S> serviceClass, String username, String password) {
        if (!TextUtils.isEmpty(username) && !TextUtils.isEmpty(password)) {
            String authToken = Credentials.basic(username, password);
            if (!TextUtils.isEmpty(authToken)) {
                AuthenticationInterceptor interceptor =  new AuthenticationInterceptor(authToken);
                if (!httpClient.interceptors().contains(interceptor)) {
                    httpClient.addInterceptor(interceptor);
                    builder.client(httpClient.build());
                    retrofit = builder.build();
                }
            }
            return retrofit.create(serviceClass);
        }else{
            return retrofit.create(serviceClass);
        }
    }

}