fix cross encoder None

app.py

@@ -111,7 +111,7 @@ with gr.Blocks() as demo:
         txt_btn = gr.Button(value="Submit text", scale=1)
 
     api_kind = gr.Radio(choices=["HuggingFace", "OpenAI"], value="HuggingFace", label="LLM")
-    cross_enc = gr.Radio(choices=["None", "cross-encoder/ms-marco-MiniLM-L-6-v2", "BAAI/bge-reranker-large"], value=None, label="Cross Encoder")
+    cross_enc = gr.Radio(choices=[None, "cross-encoder/ms-marco-MiniLM-L-6-v2", "BAAI/bge-reranker-large"], value=None, label="Cross Encoder")
 
     prompt_html = gr.HTML()
     # Turn off interactivity while generating if you click