(1) No appointment made in exercise of any power to appoint any property among two or more persons is invalid on the ground that -

(a) an insubstantial, illusory or nominal share only is appointed to or left unappointed to devolve on any one or more of those persons, or

(b) any such person is altogether excluded, whether by way of default of appointment or otherwise.

(2) This section does not affect any provision in the instrument creating the power which specifies the amount of any share from which any such person is not to be excluded.