Index: src/wp-includes/theme.php
===================================================================
--- src/wp-includes/theme.php	(revision 36344)
+++ src/wp-includes/theme.php	(working copy)
@@ -406,20 +406,18 @@
  * @staticvar array $found_themes
  *
  * @param bool $force Optional. Whether to force a new directory scan. Defaults to false.
- * @return array|false Valid themes found
+ * @return array Valid themes found
  */
 function search_theme_directories( $force = false ) {
 	global $wp_theme_directories;
-	static $found_themes = null;
+	static $found_themes = array();
 
 	if ( empty( $wp_theme_directories ) )
-		return false;
+		return array();
 
 	if ( ! $force && isset( $found_themes ) )
 		return $found_themes;
 
-	$found_themes = array();
-
 	$wp_theme_directories = (array) $wp_theme_directories;
 	$relative_theme_roots = array();