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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _handle_caption_upload( self, *, media_ids: List[str], captions: Optional[List[str]], ) -> None: """ Handle uploading all captions. :param media_ids: media ids of uploads to attach captions to. :param captions: captions to be attached to those media ids. :returns: None. """

        if captions is None:
            captions = []

        if len(media_ids) > len(captions):
            captions.extend([self.default_caption_message] * (len(media_ids) - len(captions)))

        for i, media_id in enumerate(media_ids):
            caption = captions[i]
            self._upload_caption(media_id=media_id, caption=caption)