@Override
    public Resource createRelative(String relativePath) {
        String pathToUse = StringUtils.applyRelativePath(this.path, relativePath);
        return new ClassPathResource(pathToUse, this.classLoader, this.clazz);
    }
This implementation creates a ClassPathResource, applying the given path
relative to the path of the underlying resource of this descriptor.

@return the resource.
@see spark.utils.StringUtils#applyRelativePath(String, String)
src/main/java/spark/resource/ClassPathResource.java