That would suggest for the channel that you fetched information for, there has been no bits usage.
This:
https://api.twitch.tv/helix/bits/leaderboard?period=all&count=100
Gives you the top 100 leaderboard entries for all time on the authenticated channel, but it doesn’t support pagination, so you can’t get the next page. If you specify only
https://api.twitch.tv/helix/bits/leaderboard
This means
https://api.twitch.tv/helix/bits/leaderboard?period=all&count=10
as the documentation states
Is the best method to collect bits usage really.