TYP: Make components of Suffixes Optional
The documentation on the parameters that actually are of type `Suffixes`:

> *suffixeslist-like, default is (“_x”, “_y”)*
> A length-2 sequence where each element is optionally a string indicating the suffix to add to overlapping column names in left and right respectively. _**Pass a value of None**_ instead of a string to indicate that the column name from left or right should be left as-is, with no suffix. At least one of the values must not be None.
