code: public ValueAssert valueByXPath(String xPath) {
          isNotNull();
          try {
              return ValueAssert.create(actual, prefix2Uri, dbf, xpf, xPath);
          } catch (Exception e) {
              throwAssertionError(shouldNotHaveThrown(e));
          }
          return null; //fix compile issue
      }
docs: Create {@link ValueAssert} from value of given <b>xPath</b> expression.
  
  @throws AssertionError if the xPath is blank.
  @throws AssertionError if the actual value is {@code null}.
  @throws AssertionError if the actual value provide invalid XML.