code: private JSONWriter append(String s) throws JSONException {
  
          if (s == null) {
              throw new JSONException("Null pointer");
          }
          if ((m_mode == 'o') || (m_mode == 'a')) {
              try {
                  if (m_comma && (m_mode == 'a')) {
                      m_writer.write(',');
                  }
                  m_writer.write(s);
              } catch (IOException e) {
                  throw new JSONException(e);
              }
              if (m_mode == 'o') {
                  m_mode = 'k';
              }
              m_comma = true;
              return this;
          }
          throw new JSONException("Value out of sequence.");
      }
docs: Append a value.<p>
  
  @param s a string value
  @return this
  @throws JSONException if the value is out of sequence