How to wipe out "series" field from within my metadata source plugin

[lrpirlet]

I just can't find any topic that would explain how to wipe out the "series" field from within a metadata source plugin. Sorry if I did miss the information...

If vol_serie contains a value, then the old series field for this (title, authors) gets overwritten. This is what I want.
If vol_serie is set to "" then the old series field is not wiped out, leaving a "bad" information in the series field.

        mi = Metadata(vol_title, [vol_auteur])
        mi.set_identifier('nsfr_id', self.nsfr_id)
        mi.publisher = vol_editor
        mi.isbn = vol_isbn
        mi.tags = [vol_genre]
        mi.source_relevance = self.relevance
        mi.has_cover = bool(vol_cover_index)
        if vol_dp_lgl:
            mi.pubdate = vol_dp_lgl
        mi.series = vol_serie
        if vol_serie:
            mi.series_index = vol_serie_seq
        mi.language = "fra"

        mi.comments = vol_comment_soup

        if debug: self.log.info(self.who,"mi\n",mi,"\n")
        self.plugin.clean_downloaded_metadata(mi)

        self.result_queue.put(mi)

What kind of code should I write?
Is there an example somewhere in a metadata source plugin?

Thanks in advance.

[kovidgoyal]

IIRC you cannot. Since the metadata download system assumes a null return form a plugin means data for that field was not found.

[lrpirlet]

Thanks Kovidgoyal, I was hopping for some better news, but that is ok :-)

Unless using some invisible characters such as "DEL", "NAK", "CAN", or a patern such as "DEL"*3, could be used to tell the system to force a wipeout...

However, I have not examined if that would be possible and/or if I would be able to patch calibre for that...

I guess the workaround to wipeout that field before invoking the metadata source plugin will become the rule...