def METHOD_NAME(self, adata: AnnOrMuData) -> Union[np.ndarray, pd.DataFrame]:
    """Returns the requested data as determined by the field for a given AnnData/MuData object."""
    if self.is_empty:
        raise AssertionError(f"The {self.registry_key} field is empty.")
    return get_anndata_attribute(
        adata, self.attr_name, self.attr_key, mod_key=self.mod_key
    )