def test_invalid_scalar_index(adata, index):
    # https://github.com/theislab/anndata/issues/619
    with pytest.raises(IndexError, match=r".*index.* out of range\."):
        _ = adata[index]
def serialize(self, value, display=False):
        """Convert value back to string for saving."""
        if value is None:
            return ""
        return str(value)