code: public static ByteBuffer asByteBuffer(String expression, Node node, XPath xpath)
              throws XPathExpressionException {
          String base64EncodedString = evaluateAsString(expression, node, xpath);
          if (isEmptyString(base64EncodedString)) return null;
  
          if (!isEmpty(node)) {
              byte[] decodedBytes = Base64.decode(base64EncodedString);
              return ByteBuffer.wrap(decodedBytes);
          }
          return null;
      }
docs: Same as {@link #asByteBuffer(String, Node)} but allows an xpath to be
  passed in explicitly for reuse.