Simple compile crashes with key error.

Input file:

\documentclass{scrreprt}
\pdfoutput=1

\begin{document}
foo
\end{document}

Processing command:
rubber -d minimal.tex

Traceback:

Traceback (most recent call last):
  File "/usr/local/bin/rubber", line 4, in <module>
    sys.exit(Main()(sys.argv[1:]))
  File "/usr/local/lib/python2.7/dist-packages/rubber/cmdline.py", line 319, in __call__
    return self.main(cmdline)
  File "/usr/local/lib/python2.7/dist-packages/rubber/cmdline.py", line 247, in main
    env.main.parse()
  File "/usr/local/lib/python2.7/dist-packages/rubber/converters/latex.py", line 711, in parse
    self.process(self.source())
  File "/usr/local/lib/python2.7/dist-packages/rubber/converters/latex.py", line 764, in process
    self.parse_file(file)
  File "/usr/local/lib/python2.7/dist-packages/rubber/converters/latex.py", line 742, in parse_file
    function(self.vars, *args)
  File "/usr/local/lib/python2.7/dist-packages/rubber/converters/latex.py", line 981, in h_pdfoutput
    if 'pdftex' in self.modules:
  File "/usr/local/lib/python2.7/dist-packages/rubber/converters/latex.py", line 40, in __getitem__
    return self.objects[name]
KeyError: 0