XWIKI-19948: Bad diff information when xobject is deleted (#2439)

  * Ensure to retrieve the xclass even when the xobject has been deleted
  * Ensure the BaseObject contains an XClass reference when creating it
    in XWikiDocument#getObjectDiff

(cherry picked from commit f1eaec1)

Author: surli

xwiki-platform-core/xwiki-platform-oldcore/src/main/java/com/xpn/xwiki/doc/XWikiDocument.java

@@ -7120,7 +7120,10 @@ public List<List<ObjectDiff>> getObjectDiff(XWikiDocument fromDoc, XWikiDocument
                     List<ObjectDiff> dlist;
                     if (newObj == null) {
                         // The object was deleted.
-                        dlist = new BaseObject().getDiff(originalObj, context);
+                        newObj = new BaseObject();
+                        // We want the xclass reference to be set so that it can resolve the xclass properties.
+                        newObj.setXClassReference(originalObj.getXClassReference());
+                        dlist = newObj.getDiff(originalObj, context);
                         ObjectDiff deleteMarker =
                             new ObjectDiff(originalObj.getXClassReference(), originalObj.getNumber(),
                                 originalObj.getGuid(), ObjectDiff.ACTION_OBJECTREMOVED, "", "", "", "");

xwiki-platform-core/xwiki-platform-oldcore/src/main/java/com/xpn/xwiki/objects/BaseObject.java

@@ -308,6 +308,12 @@ public List<ObjectDiff> getDiff(Object oldEntity, XWikiContext context)
             BaseProperty newProperty = (BaseProperty) this.getField(propertyName);
             BaseProperty oldProperty = (BaseProperty) oldObject.getField(propertyName);
             BaseClass bclass = getXClass(context);
+            // Bulletproofing: in theory the BaseObject is defined with a xclass reference allowing to resolve it
+            // however, it's possible that the reference is not set, in which case we might still find the info
+            // in the old object.
+            if (bclass == null) {
+                bclass = oldObject.getXClass(context);
+            }
             PropertyClass pclass = (PropertyClass) ((bclass == null) ? null : bclass.getField(propertyName));
             String propertyType = (pclass == null) ? "" : pclass.getClassType();