Update app.py

app.py

@@ -60,7 +60,7 @@ if submit_button:
     for rr in rrscore_index:
         name = df['Book Name'][topk[rr]]
         author = df['Book Author'][topk[rr]]
-        if author == "nan":
+        if author == None:
             author = "could not identify the author"
         pred_book.append(f"{name} by {author}")