Differentiate between "no data" and 0

Last night I wore my Garmin device to bed which does not track HRV, I usually wear a Fitbit that does. The trends and graphs show that my HRV last night was 0. I've seen something similar in other data fields.

I understand in some areas it's impossible to know, like if I don't log food the system doesn't know whether I didn't enter or was fasting, but for body metrics where 0 is impossible like HRV or respiratory rates it would be helpful to see that these are excluded from trends rather than dragging everything down.