Save the file model and return the model with no content.

def save(self, model, path=''):
        """Save the file model and return the model with no content."""
        if model['type'] != 'notebook':
            return super(TextFileContentsManager, self).save(model, path)

        nbk = model['content']
        try:
            metadata = nbk.get('metadata')
            rearrange_jupytext_metadata(metadata)
            jupytext_metadata = metadata.setdefault('jupytext', {})
            jupytext_formats = jupytext_metadata.get('formats') or self.default_formats(path)

            if not jupytext_formats:
                text_representation = jupytext_metadata.get('text_representation', {})
                ext = os.path.splitext(path)[1]
                fmt = {'extension': ext}

                if ext == text_representation.get('extension') and text_representation.get('format_name'):
                    fmt['format_name'] = text_representation.get('format_name')

                jupytext_formats = [fmt]

            jupytext_formats = long_form_multiple_formats(jupytext_formats, metadata)

            # Set preferred formats if not format name is given yet
            jupytext_formats = [preferred_format(fmt, self.preferred_jupytext_formats_save) for fmt in jupytext_formats]

            base, fmt = find_base_path_and_format(path, jupytext_formats)
            self.update_paired_notebooks(path, fmt, jupytext_formats)
            self.set_default_format_options(jupytext_metadata)

            if not jupytext_metadata:
                metadata.pop('jupytext')

            # Save as ipynb first
            return_value = None
            value = None
            for fmt in jupytext_formats[::-1]:
                if fmt['extension'] != '.ipynb':
                    continue

                alt_path = full_path(base, fmt)
                self.create_prefix_dir(alt_path, fmt)
                self.log.info("Saving %s", os.path.basename(alt_path))
                value = super(TextFileContentsManager, self).save(model, alt_path)
                if alt_path == path:
                    return_value = value

            # And then to the other formats, in reverse order so that
            # the first format is the most recent
            for fmt in jupytext_formats[::-1]:
                if fmt['extension'] == '.ipynb':
                    continue

                alt_path = full_path(base, fmt)
                self.create_prefix_dir(alt_path, fmt)
                if 'format_name' in fmt and fmt['extension'] not in ['.Rmd', '.md']:
                    self.log.info("Saving %s in format %s:%s",
                                  os.path.basename(alt_path), fmt['extension'][1:], fmt['format_name'])
                else:
                    self.log.info("Saving %s", os.path.basename(alt_path))
                with mock.patch('nbformat.writes', _jupytext_writes(fmt)):
                    value = super(TextFileContentsManager, self).save(model, alt_path)
                    if alt_path == path:
                        return_value = value

            # Update modified timestamp to match that of the pair #207
            return_value['last_modified'] = value['last_modified']
            return return_value

        except Exception as err:
            raise HTTPError(400, str(err))