fix changelog display which leads to a traceback

        '''

        Show changelog for a given version or all

        '''

        out('#light##yellow#Changelog:#reset#')

        # if no version take the hightest

        if version is None:

            version = max(self)

        # in non verbose mode display only asked version if exists

        if not verbose and version not in self:

            return

        out('#light##yellow#Changelog:#reset#')

        # display asked version

        out('  #yellow#Version:#reset# %s' % version)

        for line in self[version]:

            out("    %s" % line)

        if version in self:

            self._show_version(version)

        # display all version in verbose mode

        if verbose:

            for ver in sorted((k for k in self if k < version), reverse=True):

                out('  #yellow#Version:#reset# %s' % ver)

                os.linesep.join(self[ver])

                self._show_version(ver)

    def _show_version(self, version):

        '''

        Display a version content

        '''

        out('  #yellow#Version:#reset# %s' % version)

        for line in self[version]:

            out("    %s" % line)