bmake: empty list values?

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

Is there a way to specify explicitly empty values in bmake lists?
E.g. is there something I can put at **HERE** such that, in

l= x 1 y **HERE** z 2
.for i j in ${l}
	...
.endfor

j will be empty/undefined in the second iteration of the loop?
Of course, I can always work around with a magic value that can't be real 
and filter that out.