approximateCount not available in the search's response of OneDrive API/ SDK

Question

As per the specs, I should be getting @search.approximateCount field when I perform search in OneDrive. However, when I use below code/ API call:

var response = await client.Me.Drive.Root.Search(searchText).Request().GetAsync();
GET /drive/root/search(q='vacation')

I am not able to find any approximate count attribute? How can I get this count?