docs: @Override
    public final void write(final Map<String, Object> pAddParam,
      final Object pField, final String pFieldName,
        final Writer pWriter) throws Exception {
      String fieldValue;
      if (pField == null) {
        fieldValue = "NULL";
      } else {
        if (Cart.class != pField.getClass()) {
          throw new ExceptionWithCode(ExceptionWithCode
            .CONFIGURATION_MISTAKE, "It's wrong service to write that field: "
              + pField + "/" + pFieldName);
        }
        fieldValue = ((Cart) pField).getBuyer().getItsId().toString();
      }
      pWriter.write(" " + pFieldName + "=\"" + fieldValue
        + "\"\n");
    }