add children only if it's not a leaf collection

radicale/__main__.py

@@ -80,6 +80,7 @@ def export_storage(config, path, debug=False):
                         traceback.print_exc()
                     continue
                 try:
+                    if collection.is_node(collection.path):
                         remaining_collections.extend(collection.children(
                             collection.path))
                 except Exception as e: