'Out of Range' zone in heartRateZones also counts 'unknown'/0bpm heart rate minutes

[FitDevPro]

If I use API "/1/user/-/activities/heart/date/<<date>>/1d.json" I get info about the minutes in heart rate zones of that full day. 
I just wanted to know if the device is worn the whole day, so based on the API documentation I figured out that I would not need intraday access (to look at the heart rate values), but could just count how many minutes of a full day were missing from all heart rate zones combined (because there is a minimum HR) in the output of the endpoint mentioned above.
To my surprise, I noticed that the sum of minutes in all zones is always a full day, even if I did not wear the Fitbit in the evening and during the night.
Could you (the Fitbit API maintainers) please correct the minimum HR of the 'out of range' to 0 if it works that way... it does not make sense to count 0 or unknown values into that range if the minimum is 30!
An alternate fix, which would make most sense, is to actually not count 0/unknown values in that HR zone.

[DorisFitbit]

Hi @FitDevPro 

Welcome to the community! I’m sure there is a reason why we set 30 for the bottom range in the minimum heart rate zone.  It could be that the device doesn’t detect HR data below this value.  You could configure the custom heart rate zones and set the minimum bottom range value = zero.  Then use the custom heart rate zones to track your HR data.  Also, I can create a feature request to change the minimum value to zero.  If it doesn’t make sense, then we can update the documentation with the reason why.