An error occurred while executing doInBackground()

Stack trace

java.lang.RuntimeException: An error occurred while executing doInBackground()
	at android.os.AsyncTask$3.done(AsyncTask.java:318)
	at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
	at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
	at java.util.concurrent.FutureTask.run(FutureTask.java:242)
	at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
	at java.lang.Thread.run(Thread.java:761)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
	at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
	at org.json.JSONTokener.nextValue(JSONTokener.java:94)
	at org.json.JSONObject.<init>(JSONObject.java:156)
	at org.json.JSONObject.<init>(JSONObject.java:173)
	at data.JSONWeatherParser.getWeather(JSONWeatherParser.java:23)
	at com.example.bartek.weather.MainActivity$WeatherTask.doInBackground(MainActivity>.java:67)
	at com.example.bartek.weather.MainActivity$WeatherTask.doInBackground(MainActivity>.java:60)
	at android.os.AsyncTask$2.call(AsyncTask.java:304)
	at java.util.concurrent.FutureTask.run(FutureTask.java:237)
	... 4 more