Avoid a PHP notice when trying to access the `post_parent` property of hierarchical post type nav menu items.

Merges [35876] to the 4.4 branch.

Fixes #34446

Built from https://develop.svn.wordpress.org/branches/4.4@36044


git-svn-id: http://core.svn.wordpress.org/branches/4.4@36009 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-walker.php

@@ -215,7 +215,7 @@ class Walker {
 		$top_level_elements = array();
 		$children_elements  = array();
 		foreach ( $elements as $e) {
-			if ( 0 == $e->$parent_field )
+			if ( empty( $e->$parent_field ) )
 				$top_level_elements[] = $e;
 			else
 				$children_elements[ $e->$parent_field ][] = $e;

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4.1-alpha-36043';
+$wp_version = '4.4.1-alpha-36044';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.