MemcacheStore: Proper check for key-not-found.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@562 44740490-163a-0410-bde0-09ae8108e29a

lib/SimpleSAML/MemcacheStore.php

@@ -60,12 +60,12 @@ class SimpleSAML_MemcacheStore {
 		assert(self::isValidID($id));
 
 		$serializedData = SimpleSAML_Memcache::get($id);
-		$data = unserialize($serializedData);
-
-		if($data === NULL) {
-			return $NULL;
+		if($serializedData === NULL) {
+			return NULL;
 		}
 
+		$data = unserialize($serializedData);
+
 		if(!($data instanceof self)) {
 			SimpleSAML_Logger::warning('Retrieved key from memcache did not contain a MemcacheStore object.');
 			return NULL;