ProjectClassLoader.getResources(String) does not work correctly

public class ClassLoaderGetResourcesExperiment {

    public static void main(String[] args) throws IOException {
        ClassLoader classLoader = ClassLoaderGetResourcesExperiment.class.getClassLoader();
        printEnumeration(classLoader, "org/optaplanner/core/experiment");
        printEnumeration(classLoader, "org/optaplanner/core/experiment/sub1");
        printEnumeration(classLoader, "org/optaplanner/core/experiment/sub2");
        printEnumeration(classLoader, "org/optaplanner/core/experiment/sub3");
    }

    public static void printEnumeration(ClassLoader classLoader, String s) throws IOException {
        Enumeration<URL> enumeration = classLoader.getResources(s);
        System.out.println(s);
        System.out.println("================================");
        while (enumeration.hasMoreElements()) {
            Object nextElement = enumeration.nextElement();
            System.out.println("    " + nextElement);
        }
    }

}