Original commit message from CVS:
2006-04-19  Andy Wingo  <wingo@pobox.com>

* gst/arg-types.py (GstCapsArg.write_const_param)
(GstCapsArg.write_param): If there is a default value, initialize
the py_caps variable to NULL. PyArgs_Parse* doesn't touch c
variables if the optional arg isn't there. Fixes #339010.