[bugfix] NPE in NativeBroker.defragXMLResource

A regression introduced in c553667 causes a NullPointerException to be thrown whenever an XML-resource
needs to be defragmented.
This will be triggered on frequent writes to any XML-resource and will effectively remove the file
from the database and from any indexes.

exist-core/src/main/java/org/exist/storage/NativeBroker.java

@@ -3172,7 +3172,7 @@ public Object start() {
                 }
             }.run();
             // create a copy of the old doc to copy the nodes into it
-            final DocumentImpl tempDoc = new DocumentImpl(null, null, doc.getCollection(), doc.getDocId(), doc.getFileURI());
+            final DocumentImpl tempDoc = new DocumentImpl(null, pool, doc.getCollection(), doc.getDocId(), doc.getFileURI());
             tempDoc.copyOf(this, doc, doc);
             final StreamListener listener = getIndexController().getStreamListener(doc, ReindexMode.STORE);
             // copy the nodes