code: public static @Nonnull String getValue(@Nonnull String xpath, @Nonnull File file) throws IOException, SAXException, XPathExpressionException {
          return getValue(xpath, file, Charset.defaultCharset().toString());
      }
docs: The a "value" from an XML file using XPath.
  <p>
  Uses the system encoding for reading the file.
  
  @param xpath The XPath expression to select the value.
  @param file The file to read.
  @return The data value. An empty {@link String} is returned when the expression does not evaluate
  to anything in the document.
  @throws IOException Error reading from the file.
  @throws SAXException Error parsing the XML file data e.g. badly formed XML.
  @throws XPathExpressionException Invalid XPath expression.
  @since 2.0