Canon 90

Can. 90 §1. One is not to be dispensed from an ecclesiastical law without a just and reasonable cause, after taking into account the circumstances of the case and the gravity of the law from which dispensation is given; otherwise the dispensation is illicit and, unless it is given by the legislator himself or his superior, also invalid.

Can. 90 §2. In a case of doubt concerning the sufficiency of the cause, a dispensation is granted validly and licitly.