Ticket #28645: 28645.3.patch

wp-includes/default-constants.php

@@ -319 +319 @@
          * Slug of the default theme for this install.
          * Used as the default theme when installing new sites.
          * Will be used as the fallback if the current theme doesn't exist.
+         * Will use the latest theme if available, else the first theme which is returned by wp_get_themes().
          * @since 3.0.0
          */
-        if ( !defined('WP_DEFAULT_THEME') )
-                define( 'WP_DEFAULT_THEME', 'twentyfourteen' );
-
+        if ( !defined('WP_DEFAULT_THEME') ) {
+                if ( wp_get_theme('twentyfourteen')->exists() ) {               
+                        define( 'WP_DEFAULT_THEME', 'twentyfourteen' );
+                }
+                else {
+                        $themes = reset( wp_get_themes() );
+                        if ( $themes != false ) {
+                                define( 'WP_DEFAULT_THEME', $themes->get_stylesheet() );
+                        }
+                        else {
+                                define( 'WP_DEFAULT_THEME', '' );
+                        } 
+                }
+        }
 }