TypeErrors in "A quick example"

[bsiegelwax]

Describe the bug

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
[/usr/local/lib/python3.10/dist-packages/pandas/core/ops/array_ops.py](https://localhost:8080/#) in _na_arithmetic_op(left, right, op, is_cmp)
    164     try:
--> 165         result = func(left, right)
    166     except TypeError:

15 frames
TypeError: unsupported operand type(s) for /: 'str' and 'NoneType'

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call last)
[/usr/local/lib/python3.10/dist-packages/pandas/core/ops/array_ops.py](https://localhost:8080/#) in _masked_arith_op(x, y, op)
    108         # See GH#5284, GH#5035, GH#19448 for historical reference
    109         if mask.any():
--> 110             result[mask] = op(xrav[mask], yrav[mask])
    111 
    112     else:

TypeError: unsupported operand type(s) for /: 'str' and 'str'

Expected behavior
I expected to see the output on https://github.com/robertmartin8/PyPortfolioOpt

Code sample
I used the "A quick example" on https://github.com/robertmartin8/PyPortfolioOpt

Operating system, python version, PyPortfolioOpt version
Google Colab with fresh pip install

Additional context
Add any other context about the problem here.