Union value classes need to enforce non-null components

        public VlanId(Id _id) {
            super();
            this._id = _id;
            this._enumeration = null;
        }
        
        public VlanId(Enumeration _enumeration) {
            super();
            this._enumeration = _enumeration;
            this._id = null;
        }

        public VlanId(Id _id) {
            super();
            this._id = Objects.requireNonNull(_id);
            this._enumeration = null;
        }
        
        public VlanId(Enumeration _enumeration) {
            super();
            this._enumeration = Objects.requireNonNull(_enumeration);
            this._id = null;
        }