SortIndicator bug

Whenever you toggle from desc to null, the returned value to SortIndicator is asc and you could not be able to customize your own component state. When we mouse over the indicator, it displays asc even if it has not sort at all

Start at the SortIndicator entry point and reproduce the toggle from desc to null, then inspect the value passed to the indicator and its hover display. Done means an unsorted state remains null rather than becoming asc, allowing a custom component to represent that state correctly.

Written by the indexing model from the issue text.