fix default model

streamlit_app.py

@@ -254,7 +254,7 @@ with st.sidebar:
         "Model:",
         options=OPENAI_MODELS + list(OPEN_MODELS.keys()),
         index=(OPENAI_MODELS + list(OPEN_MODELS.keys())).index(
-            os.environ["DEFAULT_MODEL"]) if "DEFAULT_MODEL" not in os.environ or not os.environ["DEFAULT_MODEL"] else 0,
+            os.environ["DEFAULT_MODEL"]) if "DEFAULT_MODEL" in os.environ and os.environ["DEFAULT_MODEL"] else 0,
         placeholder="Select model",
         help="Select the LLM model:",
         disabled=st.session_state['doc_id'] is not None or st.session_state['uploaded']