if ( ! is_null( $request['customer_id'] ) && 0 !== $request['customer_id'] ) {
                // Make sure customer exists.
                if ( false === get_user_by( 'id', $request['customer_id'] ) ) {
                    throw new WC_REST_Exception( 'woocommerce_rest_invalid_customer_id', __( 'Customer ID is invalid.', 'woocommerce' ), 400 );
                }