QST: Is the behavior between "Index.astype" and "Series.astype" different ??
#### Question about pandas

When I cast the type with `astype` for `Index` or `Series`,

I noticed that their behavior for `bool` casting is slightly different.

```python
>>> pd.Series([1, None]).astype(bool)
0    True
1    True
dtype: bool

>>> pd.Index([1, None]).astype(bool)
Index([True, False], dtype='object')
```

As shown above, `None` is casted `True` from `Series.astype`, but casted `False` from `Index.astype`.

Is this normal for some reason??

I used pandas 1.1.4.

Thanks :)