fix2

app.py

@@ -83,7 +83,7 @@ class BM25Index(InvertedIndex):
     @classmethod
     def build_from_documents(
         cls: Type["BM25Index"], documents: List[Document], avgdl: float, total_docs: int, k1: float = 0.9, b: float = 0.4
-    ) -> BM25Index:
+    ) -> "BM25Index":
         # Assume run_counting() is defined to return counting object with relevant data
         counting = run_counting(documents, simple_tokenize)
         BM25Index.cache_term_weights(counting.posting_lists, total_docs, avgdl, counting.dfs, counting.dls, k1, b)