Error in request Retrofit + RxJava

I am starting with RxJava and I try to merge it with requests made with retrofit (which work correctly), but I have run into an error, which I hope can help me. I share fragments of my code:
My dependencies:

compile 'com.squareup.retrofit2:adapter-rxjava:2.1.0'
compile 'com.squareup.retrofit2:converter-gson:2.1.0'
compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
compile 'io.reactivex.rxjava2:rxjava:2.1.0'

This is the interface:

public interface Calls {
    String KEY = "AIzaSyA7m5YQp_OQXvZ7DzylErwubKq7BhIVUcs";
    String BASE_URL="https://maps.googleapis.com/";

    @GET("maps/api/place/nearbysearch/json?radius=2000&type=bank&key="+KEY)
    //Call<Basic<ArrayList<Place>>> getSities(@Query("location") String location);       //Utilizada con Retrofit
    Observable<Basic<ArrayList<Place>>> getSities(@Query("location") String location);//Utilizada con RXJava
}

RetrofitClient Class

public class RetrofitClient {
private static Retrofit retrofit = null;

public static Retrofit getClient(String baseUrl) {
    if (retrofit==null) {
        retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }
    return retrofit;
}
}

and with this I intend to obtain the data:

RetrofitClient.getClient(Calls.BASE_URL).create(Calls.class)
            .getSities(LATITUDE+","+LONGITUDE)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(places -> {                   
                rvPlacesList.setHasFixedSize(true);
                PlaceAdapterRV adapterRV = new PlaceAdapterRV(places.getResults());
                rvPlacesList.setAdapter(adapterRV);
                rvPlacesList.setLayoutManager(new LinearLayoutManager(getApplicationContext(),LinearLayoutManager.VERTICAL,false));
            });

And this is the error that throws me:

Any suggestions are welcome.