Does anyone know if it's possible to do

llm = Ollama(model="mistral")
# response = llm.complete("Who is Laurie Voss?")
# print(response)

chat_store = SimpleChatStore()

chat_memory = ChatMemoryBuffer.from_defaults(
    token_limit=3000,
    chat_store=chat_store,
    chat_store_key="user1",
)

chat_engine = SimpleChatEngine.from_defaults(llm=llm)

Traceback (most recent call last):
combat-ai  |   File "/usr/local/lib/python3.11/site-packages/llama_index/llms/utils.py", line 29, in resolve_llm
combat-ai  |     validate_openai_api_key(llm.api_key)
combat-ai  |   File "/usr/local/lib/python3.11/site-packages/llama_index/llms/openai_utils.py", line 383, in validate_openai_api_key
combat-ai  |     raise ValueError(MISSING_API_KEY_ERROR_MESSAGE)
combat-ai  | ValueError: No API key found for OpenAI.
combat-ai  | Please set either the OPENAI_API_KEY environment variable or openai.api_key prior to initialization.
combat-ai  | API keys can be found or created at https://platform.openai.com/account/api-keys
combat-ai  | 
combat-ai  | 
combat-ai  | During handling of the above exception, another exception occurred:
combat-ai  | 
combat-ai  | Traceback (most recent call last):
combat-ai  |   File "/app/app.py", line 29, in <module>
combat-ai  |     chat_engine = SimpleChatEngine.from_defaults(llm=llm)
combat-ai  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

from llama_index.core import Settings
Settings.llm=llm # Ollama instance

from llama_index import ServiceContext
from llama_index import set_global_service_context

service_context = ServiceContext(llm=llm, embed_model='BAAI/bge-small-en-v1.5`)
set_global_service_context(service_context)