Update main.py

main.py

@@ -1,5 +1,6 @@
 import os
 import json
+from typing import Optional
 from fastapi import FastAPI, HTTPException
 from pydantic import BaseModel, Field
 from huggingface_hub import InferenceClient
@@ -52,7 +53,7 @@ def format_prompt_for_text_generation(system_prompt: str, history: list, prompt:
     return out
 
 
-def chat_completion_via_http(messages: list, max_tokens: int, temperature: float, top_p: float) -> str | None:
+def chat_completion_via_http(messages: list, max_tokens: int, temperature: float, top_p: float) -> Optional[str]:
     """
     Chiamata diretta all'endpoint HF chat completions (v1).
     Usata quando il SDK fallisce perché il modello non dichiara il task (es. Ministral-3).