How do I list the sets ?

A jazz band has two star players: Mingus and Blakey. The director can choose to have one or neither, but not both, of them play in a show. In the braces below, list all the possible sets of star players that the director can have play. Write each set in your list in roster form. If there is more than one set in your list, separate them with commas. If you need the empty set in your list, use the symbol O