runtime error

Traceback (most recent call last): File "/home/user/app/app.py", line 8, in <module> os.environ['OPENAI_API_KEY'] = api_key File "/usr/local/lib/python3.10/os.py", line 685, in __setitem__ value = self.encodevalue(value) File "/usr/local/lib/python3.10/os.py", line 757, in encode raise TypeError("str expected, not %s" % type(value).__name__) TypeError: str expected, not NoneType

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