Spring ManagedSet

	@Override
	@SuppressWarnings("unchecked")
	public Set<E> merge(@Nullable Object parent) {
		if (!this.mergeEnabled) {
			throw new IllegalStateException("Not allowed to merge when the 'mergeEnabled' property is set to 'false'");
		}
		if (parent == null) {
			return this;
		}
		if (!(parent instanceof Set)) {
			throw new IllegalArgumentException("Cannot merge with object of type [" + parent.getClass() + "]");
		}
		Set<E> merged = new ManagedSet<>();
		merged.addAll((Set<E>) parent);
		merged.addAll(this);
		return merged;
	}