client/extensions/woocommerce/state/sites/settings/mailchimp/reducer.js
function settingsRequestError( state = false, action ) {
	switch ( action.type ) {
		case WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_SUCCESS:
		case WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_FAILURE:
			const error =
				WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_FAILURE === action.type ? action.error : false;
			return error;
	}

	return state;
}
function settingsRequestError( state = false, action ) {
	switch ( action.type ) {
		case WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_SUCCESS:
		case WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_FAILURE:
			const error =
				WOOCOMMERCE_MAILCHIMP_SETTINGS_REQUEST_FAILURE === action.type ? action.error : false;
			return error;
	}

	return state;
}
Updates state with settings request error
Holds information only for latest request

@param  {Object} state  Current state
@param  {Object} action Action
@return {Object}        Updated state