If declaratory relief is sought, a person who has or claims any interest which would be affected by the declaration, shall be made a party. Except in a class action, the declaration may not prejudice the rights of any person not a party to the proceeding. In any proceeding which involves the validity of a municipal or county ordinance or franchise, the municipality or county shall be made a party and is entitled to be heard. If the statute, municipal or county ordinance, or franchise is alleged to be unconstitutional, the Attorney General need not be made a party but, immediately after suit has been filed, shall be served with a copy of the proceedings by certified mail. He is entitled to be heard, submit his views in writing within a time deemed reasonable by the court, or seek intervention pursuant to the Maryland Rules.