GraphPrinter.php: fallback to getWikiValue() if getDisplayTitle() is null

For Page-type objects, use getDisplayTitle() when available;
if it returns null or empty, fall back to getWikiValue() to ensure
object text is always set.

Author: gesinn-it-ilm

src/Graph/GraphPrinter.php

@@ -216,7 +216,7 @@ protected function processResultRow( array $row ) {
 				$hasProperty = $object->getProperty();
 
 				if ( $isPageType ) {
-					$objectText = $object->getDisplayTitle();
+					$objectText = $object->getDisplayTitle() ?: $object->getWikiValue();
 				} else {
 					$objectText = $object->getWikiValue();
 				}