Update app.py

app.py

@@ -53,7 +53,7 @@ def document_retrieval_chroma(llm):
 def invoke(openai_api_key, rag, prompt):
     if (openai_api_key == ""):
         raise gr.Error("OpenAI API Key is required.")
-    if (use_rag is None):
+    if (rag is None):
         raise gr.Error("Retrieval Augmented Generation is required.")
     if (prompt == ""):
         raise gr.Error("Prompt is required.")