Can someone tell me why this code doesn't work (I get 'STARTDATE' is not a variable error):

d = createobject("clsDateRange")
d.StartDate = DATE()

***************************************
DEFINE CLASS clsDateRange AS CUSTOM
***************************************

StartDate = {}
EndDate = {}

FUNCTION IsEmpty()
RETURN (THIS.StartDate = {} AND THIS.EndDate = {})
ENDFUNC

ENDDEFINE