FIX

src/caoscrawler/sync_graph.py

@@ -471,7 +471,7 @@ class SyncGraph():
         target.update(source)
 
         # replace actual reference property values
-        for node in self.backward_references.pop(id(source)):
+        for node in self.backward_references[id(source)]:
             _set_each_scalar_value(node,
                                    condition=lambda val: val is source,
                                    value=lambda val: target)