public String getDefaultFor(int status){
        String defaultPage = defaultPages.get(status);
        return (defaultPage != null) ? defaultPage : "<html><body><h2>HTTP Status " + status + "</h2></body></html>";
    }
Returns the default error page for a given status code.
Guaranteed to never be null.
@param status
@return String representation of the default error page.
src/main/java/spark/CustomErrorPages.java