code: public static Byte asByte(String expression, Node node, XPath xpath)
              throws XPathExpressionException {
          String byteString = evaluateAsString(expression, node, xpath);
          return (isEmptyString(byteString)) ? null : Byte.valueOf(byteString);
      }
docs: Same as {@link #asByte(String, Node)} but allows an xpath to be passed
  in explicitly for reuse.