Merge branch 'bugfix/174-FSes-that-are-only-transitively-referenced-c…

…annot-be-serialized' into feature/168-Experimental-JSON-CAS-support

* bugfix/174-FSes-that-are-only-transitively-referenced-cannot-be-serialized:
  #174 - FSes that are only transitively referenced cannot be serialized (#179)

cassis/cas.py

@@ -645,7 +645,7 @@ def _find_all_fs(self, generate_missing_ids: bool = False) -> Iterable[FeatureSt
         ts = self.typesystem
         while openlist:
             fs = openlist.pop(0)
-            if generate_missing_ids:
+            if generate_missing_ids and fs.xmiID is None:
                 fs.xmiID = self._get_next_xmi_id()
             all_fs[fs.xmiID] = fs