code: public final String toJson(T value) throws IOException {
      StringWriter stringWriter = new StringWriter();
      toJson(stringWriter, value);
      return stringWriter.toString();
    }
docs: Converts {@code value} to a JSON document. Unlike Gson's similar {@link
  Gson#toJson(Object) toJson} method, this write is strict. Create a {@link
  JsonWriter#setLenient(boolean) lenient} {@code JsonWriter} and call
  {@link #write(com.socialize.google.gson.stream.JsonWriter, Object)} for lenient
  writing.
  
  @param value the Java object to convert. May be null.
  @since 2.2