def _make_series(cls, form, **kwargs):
"""Create a new :class:`EventSeries` object and save it to Mongoengine.
The event is made by creating ``series_data`` and then unpacking it
into the constructor for :class:`EventSeries`.
:param form: The WTForm form to fetch series data from.
:type form: :class:`CreateEventForm` or a subclass.
:param dict kwargs: Any other arguments that should be applied on top
of the form data.
:returns: The newly created series.
:rtype: :class:`EventSeries`
"""
series_data = DataBuilder.series_data_from_form(form)
series_data.update(kwargs)
cls._validate_series_data(series_data)
series_data = cls._remove_none_fields(series_data)
series = EventSeries(**series_data)
series.save()
return series
