Seconds in a duration string, or null if it is not one. A bad duration must
not quietly become 0 (which would read as "always stale" — noisy but wrong) nor
Infinity (silent, the failure this feature exists to end), so callers turn
null into a throw at the point the author can see it.
Seconds in a duration string, or
nullif it is not one. A bad duration must not quietly become 0 (which would read as "always stale" — noisy but wrong) norInfinity(silent, the failure this feature exists to end), so callers turnnullinto a throw at the point the author can see it.