keras/src/export/export_lib.py/ExportArchive/_get_concrete_fn
class ExportArchive:    def _get_concrete_fn(self, endpoint):
        """Workaround for some SavedModel quirks."""
        if endpoint in self._endpoint_signatures:
            return getattr(self._tf_trackable, endpoint)
        else:
            traces = getattr(self._tf_trackable, endpoint)._trackable_children(
                "saved_model"
            )
            return list(traces.values())[0]