create cursor test (f1 i)
for i = 1 to 10
	insert into test values (i)
endfor
x='1,2,3,4,5'
*!*	x=''  && uncomment to cause an error 
select * from test where iif(empty(x),.t.,f1 in (&x))
*!*	x='none'  && uncomment to cause an error 
select * from test where iif(x='none',.t.,f1 in (&x))