code: public static void json(Object obj, final String[] properties,
                              Writer writer, boolean writeClass,
                              Converter<Object, Map<String, Object>> mc) throws IOException {
          if (obj == null)
              writer.write(NULL);
          else
              json(obj, properties, new JSONWriter(writer), writeClass, mc);
      }
docs: write json.
  
  @param obj        object.
  @param properties property name array.
  @param writer     writer.
  @throws IOException.