Any person entitled to any legal character, or to any right as to any property, may institute a suit against any person denying, or interested to deny, his title to such character or right, and the court may in its discretion make therein a declaration that he is so entitled, and the plaintiff need not in such suit ask for any further relief:

   Provided that no court shall make any such declaration where the plaintiff, being able to seek further relief than a mere declaration of title, omits to do so.

   Explanation.--A trustee of property is a "person interested to deny" a title adverse to the title of some one who is not inexistence, and for whom, if in existence, he would be a trustee.