unable to pass prompt template to RetrievalQA in langchain

Question

I am new to Langchain and followed this Retrival QA - Langchain. I have a custom prompt but when I try to pass Prompt with chain_type_kwargs its throws error in pydantic StufDocumentsChain. and on removing chain_type_kwargs itt just works.

how can pass to the prompt?

error

File /usr/local/lib/python3.11/site-packages/pydantic/main.py:341, in pydantic.main.BaseModel.__init__()

ValidationError: 1 validation error for StuffDocumentsChain
__root__
  document_variable_name context was not found in llm_chain input_variables: ['question'] (type=value_error)

Code

import json, os

from langchain.chains import RetrievalQA
from langchain.llms import OpenAI
from langchain.document_loaders import JSONLoader
from langchain.text_splitter import CharacterTextSplitter
from langchain.embeddings.openai import OpenAIEmbeddings
from langchain.vectorstores import Chroma
from langchain.chat_models import ChatOpenAI
from langchain import PromptTemplate

from pathlib import Path
from pprint import pprint




os.environ["OPENAI_API_KEY"] = "my-key"



def metadata_func(record: dict, metadata: dict) -> dict:
    metadata["drug_name"] = record["drug_name"]

    return metadata


loader = JSONLoader(
    file_path='./drugs_data_v2.json', 
    jq_schema='.drugs[]',
    content_key="data",
    metadata_func=metadata_func)

docs = loader.load()


text_splitter = CharacterTextSplitter(chunk_size=5000, chunk_overlap=200)
texts = text_splitter.split_documents(docs)


embeddings = OpenAIEmbeddings()

docsearch = Chroma.from_documents(texts, embeddings)


template = """/
example custom prommpt

Question: {question}
Answer: 
"""

PROMPT = PromptTemplate(template=template, input_variables=['question'])


qa = RetrievalQA.from_chain_type(
        llm=ChatOpenAI(
           model_name='gpt-3.5-turbo-16k'       
    ),
    chain_type="stuff",
    chain_type_kwargs={"prompt": PROMPT},
    retriever=docsearch.as_retriever(),
)

query = "What did the president say about Ketanji Brown Jackson"
qa.run(query)

Answer 1

{context} is missing in template.