Is it good or bad practice to publish metrics with a value of 0 if they haven't been seen in a paritcular time window

See discussion here https://gitter.im/kamon-io/Kamon?at=5d0f51b37456db0bb83e8a18 But the tl;dr is that Kamon (a tool for measuring and reporting opentracing spans) reports the fact that a particular span HASN’T occurred. See https://pastebin.com/r2FAZn1Y for an example.

My question is, is this a bad practice?