Hi That is nicely written guides. I have a question: For below codes; from llama_index import VectorStoreIndex, SimpleDirectoryReader #Load documents from a directory documents = SimpleDirectoryReader('book').load_data() #Create an index from the documents index=VectorStoreIndex.from_documents(documents) i have an exception thrown at this line:VectorStoreIndex.from_documents(..) No API key found for OpenAI. Please set either the OPENAI_API_KEY environment variable or openai.api_key prior to initialization. API keys can be found or created at ..... I am just testing the indexing, and i am not using openai. Why was there an openai exception when the app is executing this line: VectorStoreIndex.from_documents(documents)?