Update backend/query_llm.py

backend/query_llm.py

@@ -143,7 +143,8 @@ def generate_openai(prompt: str, history: str, temperature: float = 0.9, max_new
                                                 stream=True)
         output = ""
         for chunk in stream:
-            output += chunk.choices[0].delta.content
+            if chunk.choices[0].delta.content is not None:
+                output += chunk.choices[0].delta.content
             yield output
 
     except Exception as e: