an integer or string of size 1 is required exception - android-asynctask

Question

I was trying a sketch program found online that connects wirelessly to my Raspberry pi using HttpURLConnection.. it's catching the exception "an integer or string of size 1 is required" and i dunno where's the error yet. The program basically sends a character or number when the user hits a button on UI to the webserver running on Raspberry pi. here's a part of the send command:
private void sendCommand(String command) {
final String cmd = command;
AsyncTask task = new AsyncTask() {
private String resp;
#Override
protected Object doInBackground(Object... params) {
try {
resp = Sender.getStringResponseFromGetRequest(
"http://192.168.1.111:8888/" + cmd);
} catch (IOException e) {
resp = e.getMessage();
}
return null;
}
};
}
#Override
protected void onPostExecute(Object result) {
if(!resp.equals("OK")){
Toast.makeText(ctx, resp, Toast.LENGTH_LONG).show();
}
super.onPostExecute(result);
}
};
task.execute();
}
}
and here's the getStringResponse.. Method:
public static String getStringResponseFromGetRequest(String requestUrl)
throws IOException {
URL url1;
URLConnection urlConnection;
DataInputStream inStream;
url1 = new URL(requestUrl);
urlConnection = url1.openConnection();
((HttpURLConnection) urlConnection).setRequestMethod("GET");
urlConnection.setDoInput(true);
urlConnection.setDoOutput(false);
urlConnection.setUseCaches(false);
inStream = new DataInputStream(urlConnection.getInputStream());
return inStream.readLine();
}