Post Thumbnails: In `get_the_post_thumbnail_url()`, return `false` instead of empty string when no URL is available.

Fixes #33070.

Built from https://develop.svn.wordpress.org/trunk@34480


git-svn-id: http://core.svn.wordpress.org/trunk@34444 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/post-thumbnail-template.php

@@ -179,11 +179,11 @@ function get_the_post_thumbnail( $post = null, $size = 'post-thumbnail', $attr =
  * @param int|WP_Post  $post Optional. Post ID or WP_Post object.  Default is global `$post`.
  * @param string|array $size Optional. Registered image size to retrieve the source for or a flat
  *                           array of height and width dimensions. Default 'post-thumbnail'.
- * @return string Post thumbnail URL or empty string.
+ * @return string|false Post thumbnail URL or false if no URL is available.
  */
 function get_the_post_thumbnail_url( $post = null, $size = 'post-thumbnail' ) {
 	$image = wp_get_attachment_image_url( get_post_thumbnail_id( $post ), $size );
-	return isset( $image ) ? $image : '';
+	return isset( $image ) ? $image : false;
 }
 
 /**

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34479';
+$wp_version = '4.4-alpha-34480';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.