code: def validate_environment(api_key):
      if api_key is None:
          raise ValueError(
              "Missing AI21 API Key - A call is being made to ai21 but no key is set either in the environment variables or via params"
          )
      headers = {
          "accept": "application/json",
          "content-type": "application/json",
          "Authorization": "Bearer " + api_key,
      }
      return headers
  
file_path: litellm/litellm/llms/ai21.py
imports: import os, types, traceback
  import json
  from enum import Enum
  import requests
  import time, httpx
  from typing import Callable, Optional
  from litellm.utils import ModelResponse, Choices, Message
  import litellm
label_desc: Use image node_id 1 for calling a global function with example usage: validate_environment(api_key) and returns: headers