#fixed code
                                private static List<Constructor<?>> getRipperConstructors() throws Exception {
        List<Constructor<?>> constructors = new ArrayList<Constructor<?>>();
        for (Class<?> clazz : getClassesForPackage("com.rarchives.ripme.ripper.rippers")) {
            if (AbstractRipper.class.isAssignableFrom(clazz)) {
                constructors.add( (Constructor<?>) clazz.getConstructor(URL.class) );
            }
        }
        return constructors;
    }
#vulnerable code 
                                private static List<Constructor<?>> getRipperConstructors() throws Exception {
        List<Constructor<?>> constructors = new ArrayList<Constructor<?>>();
        String rippersPackage = "com.rarchives.ripme.ripper.rippers";
        ClassLoader cl = Thread.currentThread().getContextClassLoader();
        Enumeration<URL> urls = cl.getResources(rippersPackage.replaceAll("\\.", "/"));
        if (!urls.hasMoreElements()) {
            return constructors;
        }
        URL classURL = urls.nextElement();
        for (File f : new File(classURL.toURI()).listFiles()) {
            String className = f.getName();
            if (!className.endsWith(".class")
                    || className.contains("$")
                    || className.endsWith("Test.class")) {
                // Ignore non-class or nested classes.
                continue;
            }
            className = className.substring(0, className.length() - 6); // Strip .class
            String fqname = rippersPackage + "." + className;
            Class<?> clazz = Class.forName(fqname);
            constructors.add( (Constructor<?>) clazz.getConstructor(URL.class));
        }
        return constructors;
    } 
                            #location 10 
                            #vulnerability type NULL_DEREFERENCE