AttributeError: st.session_state has no attribute "retriever".

[twocoins-ca]

AttributeError: st.session_state has no attribute "retriever". Did you forget to initialize it? More info: https://docs.streamlit.io/library/advanced-features/session-state#initialization
Traceback:
File "/home/devsecops/projects/Retrieval-Augmented-Generation-Engine-with-LangChain-and-Streamlit/.venv/lib/python3.10/site-packages/streamlit/runtime/scriptrunner/script_runner.py", line 552, in _run_script
exec(code, module.dict)
File "/home/devsecops/projects/Retrieval-Augmented-Generation-Engine-with-LangChain-and-Streamlit/rag_engine.py", line 137, in
boot()
File "/home/devsecops/projects/Retrieval-Augmented-Generation-Engine-with-LangChain-and-Streamlit/rag_engine.py", line 132, in boot
response = query_llm(st.session_state.retriever, query)
File "/home/devsecops/projects/Retrieval-Augmented-Generation-Engine-with-LangChain-and-Streamlit/.venv/lib/python3.10/site-packages/streamlit/runtime/state/session_state_proxy.py", line 121, in getattr
raise AttributeError(_missing_attr_error_message(key))