我如何处理或删除此异常

Question

如何处理此java.lang.IllegalStateException

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            getCurrentdata();
        }
    });
}
private void getCurrentdata() {
    String url = Serverfetcheddata.base_url+"data/2.5/weather?q="+ city_name.getText().toString() + "&appid=" +Serverfetcheddata.key;
    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(Serverfetcheddata.base_url)
            .addConverterFactory(GsonConverterFactory.create())
            .build();
    Serverfetcheddata serverfetcheddata = retrofit.create(Serverfetcheddata.class);
    Call<Weather> weatherCall = serverfetcheddata.getCurrentWeatherData(url);
    weatherCall.enqueue(new Callback<Weather>() {
        @Override
        public void onResponse(Call<Weather> call, Response<Weather> response) {
           Weather weather = response.body();
            fetch_data.setText(weather.getMain());
           // fetch_data.setText(weather.getMain());
           // Toast.makeText(MainActivity.this, "Success"+ " "+ response.body(), Toast.LENGTH_SHORT).show();
        }
        @Override
        public void onFailure(Call<Weather> call, Throwable t) {
            Log.d("CODE","Error Message :"+t.getMessage());
            //fetch_data.setText(t.getMessage());
        }
    });
}

}

错误消息：java.lang.IllegalStateException：应为字符串，但为  第1行第133列的BEGIN_OBJECT路径$ .main