Android : null pointer exception while working in device but not in emulator

I got Null value in jsonBranchArray while working in device. But I got value for the same while working in emulator.

  String jsonBranchArray = appUtils
                            .getDataFromUrl("---URL---");

And AppUtils class is..

  public class AppUtils {


 public String getDataFromUrl(String url) {

     BufferedReader reader = null;
     String str = null;

     try {

     URL url2 = new URL(url);
     InputStream ins = url2.openStream();
     reader = new BufferedReader(new InputStreamReader(ins));
     StringBuilder builder = new StringBuilder();
     while ((str = reader.readLine()) != null) {
     builder.append(str);
     }
     str = builder.toString();
     } catch (Exception e) {
     e.printStackTrace();
     str = null;
     } finally {
     if (reader != null) {
     try {
     reader.close();
     } catch (IOException e) {
     e.printStackTrace();
     }
     }
     }
     return str;
     }}

Please help on it. Thanks in advance.