Did not find openai_api_key, please add an environment variable `OPENAI_API_KEY` which contains it, or pass  `openai_api_key` as a named parameter. (type=value_error)
Labels: name: auto:bug

### System Info

I am trying to build a **VectorstoreIndexCreator** using the following configuration

embeddings= **SentenceTransformerEmbeddings** embeddings
vectorstore_cls  = **Chroma**
llm = **HuggingfaceHub** Model

Note: I am not using any **openai** model as **llm** or **embedding** purpose

here is the code
```
  from langchain.indexes import VectorstoreIndexCreator
  from langchain.vectorstores import Chroma
  from langchain.text_splitter import CharacterTextSplitter
  from langchain.embeddings import SentenceTransformerEmbeddings
  from langchain.llms import HuggingFaceHub
  from langchain.document_loaders import PyPDFLoader
  loader = PyPDFLoader("pdffile.pdf")

  embeddings =  SentenceTransformerEmbeddings(model_name="paraphrase-MiniLM-L6-v2")
  model = HuggingFaceHub(repo_id="facebook/mbart-large-50",
                       model_kwargs={"temperature": 0, "max_length":200},
                       huggingfacehub_api_token=HUGGING_FACE_API_KEY)
  index = VectorstoreIndexCreator(
                                  embeddings=embeddings,
                                  vectorstore_cls=Chroma,
                                  text_splitter=CharacterTextSplitter(chunk_size=100,chunk_overlap=0)
                                  ).from_loaders([loader])
  result = index.query(llm=model,qustion=query,chain_type="refine")
```
But still iam getting the open_ai key dependency error when i run the code
```
Did not find openai_api_key, please add an environment variable `OPENAI_API_KEY` which contains it, or pass  `openai_api_key` as a named parameter. (type=value_error)
```

using langchain version: **langchain==0.0.219**


### Who can help?

_No response_

### Information

- [ ] The official example notebooks/scripts
- [X] My own modified scripts

### Related Components

- [X] LLMs/Chat Models
- [X] Embedding Models
- [ ] Prompts / Prompt Templates / Prompt Selectors
- [ ] Output Parsers
- [ ] Document Loaders
- [ ] Vector Stores / Retrievers
- [ ] Memory
- [X] Agents / Agent Executors
- [ ] Tools / Toolkits
- [ ] Chains
- [ ] Callbacks/Tracing
- [ ] Async

### Reproduction

 ``` 
 from langchain.indexes import VectorstoreIndexCreator
  from langchain.vectorstores import Chroma
  from langchain.text_splitter import CharacterTextSplitter
  from langchain.embeddings import SentenceTransformerEmbeddings
  from langchain.llms import HuggingFaceHub
  from langchain.document_loaders import PyPDFLoader
  loader = PyPDFLoader("pdffile.pdf")

  embeddings =  SentenceTransformerEmbeddings(model_name="paraphrase-MiniLM-L6-v2")
  model = HuggingFaceHub(repo_id="facebook/mbart-large-50",
                       model_kwargs={"temperature": 0, "max_length":200},
                       huggingfacehub_api_token=HUGGING_FACE_API_KEY)
  index = VectorstoreIndexCreator(
                                  embeddings=embeddings,
                                  vectorstore_cls=Chroma,
                                  text_splitter=CharacterTextSplitter(chunk_size=100,chunk_overlap=0)
                                  ).from_loaders([loader])
  result = index.query(llm=model,qustion=query,chain_type="refine")
```

### Expected behavior

Dont show any openai error