WooCommerce field validation

add_action('woocommerce_checkout_process', 'pcr_custom_checkout_field_process');
function pcr_custom_checkout_field_process() {

    //validating if a drop-down is filled in

    if ( $_POST['need_booth_space'] == 'blank' ) {
        wc_add_notice( __( 'Please select if you will need booth space at the event.' ), 'error' );
    }

    //validating if a text field is filled in

    if ( ! $_POST['display_theme'] ) {
        wc_add_notice( __( 'Please fill in the display theme of your booth at the event.' ), 'error' );
    }
}