code: public DataUrl build() throws NullPointerException {
          if (data == null) {
              throw new NullPointerException("data is null!");
          } else if (encoding == null) {
              throw new NullPointerException("encoding is null!");
          }
          return new DataUrl(data, encoding, mimeType, headers);
      }
docs: Creates a new {@link DataUrl} instance
  @return New {@link DataUrl} instance
  @throws NullPointerException if data or encoding is {@code null}