def _to_dict(self):
        """
        Internal method that serializes object into a dictionary.
        """
        data = {
            'name': self.name,
            'referenceId': self.reference_id,
            'shortDescription': self.short_description,
            'playlistType': self.type,
            'id': self.id}
        if self.videos:
            for video in self.videos:
                if video.id not in self.video_ids:
                    self.video_ids.append(video.id)
        if self.video_ids:
            data['videoIds'] = self.video_ids
        [data.pop(key) for key in data.keys() if data[key] == None]
        return data
Internal method that serializes object into a dictionary.