Index: class.t3lib_page.php
===================================================================
--- class.t3lib_page.php	(revision 9019)
+++ class.t3lib_page.php	(working copy)
@@ -738,6 +738,9 @@
 			$output[$c] = $val;
 		}
 
+        //if $MP is empty, $MP get an default value
+        if (is_empty($MP) or ($MP === '')) { $MP = 0; }
+        
 			// Note: rootline errors are not cached
 		$this->cache_getRootLine[$cacheUid][$this->sys_language_uid][$MP][$cacheIgnoreMPerrors] = $output;
 		return $output;