final ElementCustomization annotation = customizer.getClass().getAnnotation(ElementCustomization.class);
if (annotation == null) {
throw new IllegalStateException("Customizer " + customizer.getClass().getName() + " doesn't have " +
ElementCustomization.class.getName() + " annotation");
}
final String target = annotation.target();
if (!customizers.containsKey(target)) {
customizers.put(target, new ArrayList<Object>());
}
customizers.get(target).add(customizer);
}