Number of values returned when using the time frequency (created_utc) aggregation is inconsistent

[BravoTangoCharlie09]

If I am searching for the number of times "trump" is mentioned in new submissions for every minute over the last hour, it should return 60 values.

Specifically, I am using: https://api.pushshift.io/reddit/search/submission/?q=*&after=2h&aggs=created_utc&frequency=minute&size=0&subreddit=bitcoin

I am using this to graph the volume new submissions for bitcoin vs timestamp data. However, it always returns different lengths for the time period when it should return a specific length (when there are no new submissions for a time period it should show "0")