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:
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.