code: def test_validate_environment_empty_model():
      api_key = validate_environment()
      if api_key is None:
          raise Exception()
  
imports: import sys, os
  from dotenv import load_dotenv
  import copy
  import os
  import pytest
  import litellm
  from litellm.utils import trim_messages, get_token_count, get_valid_models, check_valid_key, validate_environment, function_to_dict, token_counter
label_desc: Use image node_id 13 for calling a global function with example usage: test_validate_environment_empty_model() without return types