X-Git-Url: https://git.mdrn.pl/librarian.git/blobdiff_plain/7231c2b5e9364aefd27a0bc8a1033de90bb3d878..2991698067a246ea9b99b4e668d261af6d418eca:/src/librarian/document.py

diff --git a/src/librarian/document.py b/src/librarian/document.py
index ea8a47a..6ac2842 100644
--- a/src/librarian/document.py
+++ b/src/librarian/document.py
@@ -40,9 +40,9 @@ class WLDocument:
     def build(self, builder, base_url=None, **kwargs):
         return builder(base_url=base_url).build(self, **kwargs)
 
-    def assign_ids(self):
+    def assign_ids(self, existing=None):
         # Find all existing IDs.
-        existing = set()
+        existing = existing or set()
         que = [self.tree.getroot()]
         while que:
             item = que.pop(0)