pyparsing: crash on empty element

[gry at ll.mit.edu]

[python 2.3.3, pyparsing 1.3]
I have:

 def unpack_sql_array(s):
    # unpack a postgres "array", e.g. "{'w1','w2','w3'}" into a
list(str)
    import pyparsing as pp
    withquotes = pp.dblQuotedString.setParseAction(pp.removeQuotes)
    withoutquotes = pp.CharsNotIn('",{}')
    parser = pp.StringStart() + \
             pp.Literal('{').suppress() + \
             pp.delimitedList(withquotes | withoutquotes) + \
             pp.Literal('}').suppress() + \
             pp.StringEnd()
    return parser.parseString(s).asList()

which works beautifully, except on the input: "{}".  How can I neatly
modify the parser to return an empty list in this case?
Yes, obviously, I could say
   if s=='{}': return []
It just seems like I'm missing some simple intrinsic way to get this
out of the parser.  I am hoping to become more skillful in using the
wonderful pyparsing module!

-- George Young