List Box Parameter

Khoza

Morning folks

Folks i'm having list box parameter that i have populated with values and the parameter is not a required parameter therefore the diplay text of the list box parameter is Null Value as the default display text and the rest of the values populated. My problem is i'm actually struggling to change the display text "Null Value" to a descriptive text called "(all merchants)" instead of "Null Value". Please help it is urgent.

Thanking you in advance

Regards,
Lucky Khoza