Runtime error: if zone.upper() == 'UTC': AttributeError: 'numpy.float64' object has no attribute 'upper'

**Describe the bug**
first run Stock_NeurIPS2018_SB3.py error

**To Reproduce**
Steps to reproduce the behavior:
cmd run :python Stock_NeurIPS2018_SB3.py

**Screenshots**
(AI4Finance) D:\GoData\src\github.com\AI4Finance-Foundation\FinRL>python Stock_NeurIPS2018_SB3.py
D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\pyfolio\pos.py:26: UserWarning: Module "zipline.assets" not found; multipliers will not be applied to position notionals.
warnings.warn(
Exception in thread Thread-1:
Traceback (most recent call last):
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\threading.py", line 980, in _bootstrap_inner
self.run()
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\threading.py", line 917, in run
self._target(*self._args, **self._kwargs)
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\multitasking\__init__.py", line 104, in _run_via_pool
return callee(*args, **kwargs)
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\yfinance\multi.py", line 199, in _download_one_threaded
data = _download_one(ticker, start, end, auto_adjust, back_adjust,
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\yfinance\multi.py", line 213, in _download_one
return Ticker(ticker).history(period=period, interval=interval,
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\yfinance\base.py", line 168, in history
end = utils._parse_user_dt(end, tz)
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\yfinance\utils.py", line 157, in _parse_user_dt
dt = _tz.timezone(exchange_tz).localize(dt)
File "D:\ProgramData\Anaconda3\envs\AI4Finance\lib\site-packages\pytz\__init__.py", line 170, in timezone
if zone.upper() == 'UTC':
AttributeError: 'numpy.float64' object has no attribute 'upper'