code: public Object parseAs(Type dataType) throws IOException {
      if (!hasMessageBody()) {
        return null;
      }
      return request.getParser().parseAndClose(getContent(), getContentCharset(), dataType);
    }
docs: Parses the content of the HTTP response from {@link #getContent()} and reads it into a data
  type of key/value pairs using the parser returned by {@link HttpRequest#getParser()}.
  
  @return parsed data type instance or {@code null} for no content
  @since 1.10