do nothing, if title == null

Author: gesinn-it-gea

Diff for: SemanticDependencyUpdater.hooks.php

@@ -23,8 +23,7 @@ public static function setup() {
 		}
 	}
 
-	public static function onAfterDataUpdateComplete( SMWStore $store, SMWSemanticData $newData,
-													  $compositePropertyTableDiffIterator ) {
+	public static function onAfterDataUpdateComplete( SMWStore $store, SMWSemanticData $newData, $compositePropertyTableDiffIterator ) {
 		global $wgSDUProperty;
 		global $wgSDUTraversed;
 
@@ -35,6 +34,10 @@ public static function onAfterDataUpdateComplete( SMWStore $store, SMWSemanticDa
 		$wgSDUProperty = str_replace( ' ', '_', $wgSDUProperty );
 		$subject = $newData->getSubject();
 		$title = $subject->getTitle();
+		if ($title == null) {
+			return true;
+		}
+
 		$id = $title->getPrefixedDBKey();
 
 		wfDebugLog( 'SemanticDependencyUpdater', "[SDU] --> " . $title );