Where the court grants a decree of dissolution (within the meaning of Part 12), it may declare either of the civil partners concerned to be unfit to have custody of any dependent child of the civil partners who is under the age of 18 years and, if it does so and the civil partner to whom the declaration relates is a parent of any dependent child of the civil partners who is under the age of 18 years, that civil partner shall not, on the death of the other civil partner, be entitled as of right to the custody of that child.