Hi Guys, I , again sadly, met the same "Under no circumstances should null be returned." error in this problem. I have no idea on why this error constantly throws out. Any advice ?! Thank you! 
public class Solution {
    public static void main(String[] args) throws IOException {
        StringWriter writer = getAllDataFromInputStream(new FileInputStream("testFile.log"));
        System.out.println(writer.toString());
    }

    public static StringWriter getAllDataFromInputStream(InputStream is) throws IOException {
        StringWriter stringWriter = new StringWriter();
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        try{
            String line;
            while ((line = reader.readLine()) != null){
                stringWriter.write(line);
            }
        }
        catch (IOException e){}
        reader.close();
        return stringWriter;
    }
}