Products without image should display WooCommerce’s placeholder image.

I think that in order to be more compliant to WooCommerce, the template for the products in the “shop” section in the front page could use like in woocommerce/single-product/product-image.php:

if ( has_post_thumbnail() ) {
			$html  = '<div data-thumb="' . get_the_post_thumbnail_url( $post->ID, 'shop_thumbnail' ) . '" class="woocommerce-product-gallery__image"><a href="' . esc_url( $full_size_image[0] ) . '">';
			$html .= get_the_post_thumbnail( $post->ID, 'shop_single', $attributes );
			$html .= '</a></div>';
		} else {
			$html  = '<div class="woocommerce-product-gallery__image--placeholder">';
			$html .= sprintf( '<img src="%s" alt="%s" class="wp-post-image" />', esc_url( wc_placeholder_img_src() ), esc_html__( 'Awaiting product image', 'woocommerce' ) );
			$html .= '</div>';
		}