private boolean isNoValueSupplier(CollectionSupplier<T, C> valueSupplier) {
        // Cannot use plain NoValueSupplier because of Java restrictions:
        // a generic type [AbstractCollectionProperty<T, C>.]NoValueSupplier cannot be used in instanceof.
        return valueSupplier instanceof AbstractCollectionProperty<?, ?>.NoValueSupplier;
    }

    @Override
    public void add(final T element) {

    }

    private void init() {
        defaultValue = emptySupplier();
        init(defaultValue, noValueSupplier());
    }

    @Override
    public MapSupplier<K, V> getDefaultValue() {
        return defaultValue;
    }

    @Override
    protected MapSupplier<K, V> getDefaultConvention() {
        return noValueSupplier();
    }

    @Override
    protected boolean isDefaultConvention() {