You win a free upgrade. Yup, it's a bug. It applies to simple SET macros as well.
Easy to fix. In line 125 of parse.mma right after:
while 1:
curline = inpath.read()
if curline is None: # eof, exit parser
break
l = macros.expand(curline)
add the lines:
if not l:
continue
This way empty macros are skipped over. BTW, if you are new to python make sure you have proper indentation (which doesn't show up here). Shout if you need help.