WooCommerce: User parent product's description if child product's description is empty

functions.php

<?php
/**
 * Iconic SSV: use parent's description if child product's description is empty.
 *
 * @param string $description
 * @param object $product
 *
 * @return string
 */
function iconic_ssv_modify_variation_description( $description, $product ) {
	if ( ! $product->is_type( 'variation' ) || ! empty( $description ) ) {
		return $description;
	}

	// get parent products description.
	$parent_id      = $product->get_parent_id();
	$parent_product = wc_get_product( $parent_id );

	if ( ! $parent_product ) {
		return $description;
	}

	return $parent_product->get_description();
}
add_filter( 'woocommerce_product_variation_get_description', 'iconic_ssv_modify_variation_description', 10, 2 );