dotenv.load_dotenv()
os.environ['OPENAI_BASE_URL'] = os.getenv("OPENAI_BASE_URL")
os.environ['OPENAI_API_KEY'] = os.getenv("OPENAI_API_KEY")

This is my code piece, it output "TypeError Traceback (most recent call last)" in line 2. However, it operated well in .py and I wonder why.

File D:\Programs\miniconda3\envs\pyth310\lib\os.py:685, in _Environ.__setitem__(self, key, value)
    683 def __setitem__(self, key, value):
    684     key = self.encodekey(key)
--> 685     value = self.encodevalue(value)
    686     putenv(key, value)
    687     self._data[key] = value

File D:\Programs\miniconda3\envs\pyth310\lib\os.py:743, in _createenviron..check_str(value)
    741 def check_str(value):
    742     if not isinstance(value, str):
--> 743         raise TypeError("str expected, not %s" % type(value).__name__)
    744     return value

TypeError: str expected, not NoneType