  private String attributeToString(Object attribute) {
    if (attribute == null) {
      return null;
    }

    if (attribute instanceof Number) {
      return attribute.toString();
    } else if (attribute instanceof String) {
      return (String) attribute;
    } else if (attribute instanceof Element) {
      return ((Element) attribute).getTextContent();
    } else {
      logger.warn("This library currently doesn't handle attributes of type [" + attribute.getClass() + "]");
    }

    return null;
  }
The software processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.