docs: public @Nonnull XQuery get(String xpath) {
          NodeList nl = evaluate(xpath);
          if (nl.getLength() == 1) {
              return new XQuery(nl.item(0));
          } else if (nl.getLength() == 0) {
              throw new IllegalArgumentException("XPath '" + xpath
                  + "' does not match any elements");
          } else {
              throw new IllegalArgumentException("XPath '" + xpath + "' matches "
                  + nl.getLength() + " elements");
          }
      }