XWIKI-19092: Null object can make the document rename fail

(cherry picked from commit efcbd568)

xwiki-platform-core/xwiki-platform-refactoring/xwiki-platform-refactoring-default/src/main/java/org/xwiki/refactoring/internal/DefaultLinkRefactoring.java

@@ -160,7 +160,9 @@ private void renameLinks(XWikiDocument document, DocumentReference oldTarget, Do
         // XObjects properties
         for (List<BaseObject> xobjects : document.getXObjects().values()) {
             for (BaseObject xobject : xobjects) {
-                modified |= renameLinks(xobject, document, oldTarget, newTarget, renderer, xcontext, relative);
+                if (xobject != null) {
+                    modified |= renameLinks(xobject, document, oldTarget, newTarget, renderer, xcontext, relative);
+                }
             }
         }