def add_missing(self, distribution, requirement):
logger.debug('<STR_LIT>', distribution, requirement)<EOL>self.missing.setdefault(distribution, []).append(requirement)<EOL>
Add a missing *requirement* for the given *distribution*.

:type distribution: :class:`distutils2.database.InstalledDistribution`
                    or :class:`distutils2.database.EggInfoDistribution`
:type requirement: ``str``