fix function get_similarity_doc bug

src/controller/web.py

@@ -321,6 +321,8 @@ def get_similarity_doc(similarity_doc_hash: str):
     txt_doc = TxtDoc(k_db)
     for h in hashs:
         doc = txt_doc.search(h)
+        if doc is None:
+            continue
         d = Document(page_content=doc[0],metadata=json.loads(doc[1]))
         docs.append(d)    
     return docs_to_json(docs)