Ticket #20004: 20004.notices.diff

wp-includes/cache.php

@@ -534 +534 @@
          * @access private
          */
         protected function _exists($key, $group) {
-                return is_array( $this->cache[$group] ) && array_key_exists( $key, $this->cache[$group] );
+                return isset( $this->cache[$group] ) && is_array( $this->cache[$group] ) && array_key_exists( $key, $this->cache[$group] );
         }
 
         /**