Unhealthy Checks have Optional when reporting the threshold

[dexhorthy]

Error message used to be pretty easy to parse programmatically:

value=1.0&ceiling=0.2

It now displays the ceiling wrapped in an Optional:

value=1.0&ceiling=Optional[0.2]

This is probably pretty minor, as anyone who's parsing the result--e.g. to implement their own warn vs. crit thresholds--is probably looking at the value more often than the ceiling.