Set a WooCommerce custom default thumbnail and avoid mixed-content errors with SSL

woocommerce-change-default-thumbnail.php

/**
* Change default thumbnail 
* @since 1.0
* @author Gabe Lloyd 
* ref: https://core.trac.wordpress.org/ticket/25449
*/
add_action( 'init', 'custom_fix_thumbnail' );
 
function custom_fix_thumbnail() {
  add_filter('woocommerce_placeholder_img_src', 'custom_woocommerce_placeholder_img_src');
   
	function custom_woocommerce_placeholder_img_src( $src ) {
	$upload_dir = wp_upload_dir();
	$baseurl = untrailingslashit( $upload_dir['baseurl'] );
	$set_url_scheme = set_url_scheme( $baseurl ); // this is required to avoid mixed-content errors on SSL installs
	$src = $set_url_scheme . '/2017/04/coming-soon.png'; // replace this with the image you want to use
	 
	return $src;
	}
}