Create a procedure to add $0$ to the invoice column if it is null. Select the correct SQL$.$

a$.$ CREATE OR REPLACE PROCEDURE CHECK$\_$INVOICE

AS BEGIN

UPDATE Appointments

SET INVOICE $=0$

WHERE INVOICE IS NULL;

DBMS$\_$OUTPUT.PUTLINE$("$Update completed"$)$;

END;

b$.$ UPDATE Appointments

SET INVOICE $=0$;

c$.$ CREATE OR REPLACE PROCEDURE CHECK$\_$INVOICE

AS BEGIN

UPDATE Appointments

SET INVOICE $=0$

WHERE INVOICE $=$ NULL;

DBMS$\_$OUTPUT.PUTLINE$(\text{'}$Update completed'$)$;

END;