code: public static void ensureXPathNotNull(Node node, String expression) {
      if (node == null) {
        throw LOG.unableToFindXPathExpression(expression);
      }
    }
docs: Ensure that the node is not null.
  
  @param node the node to ensure to be not null
  @param expression the expression was used to find the node
  @throws SpinXPathException if the node is null