def METHOD_NAME(
    self, state_registry: dict, adata_target: AnnData, **kwargs
) -> dict:
    """Transfer the field."""
    super().METHOD_NAME(state_registry, adata_target, **kwargs)
    n_vars = state_registry[self.N_VARS_KEY]
    target_n_vars = adata_target.n_vars
    if target_n_vars != n_vars:
        raise ValueError(
            "Number of vars in adata_target not the same as source. "
            + f"Expected: {target_n_vars} Received: {n_vars}"
        )
    return self.register_field(adata_target)