jvm.memory.non-heap.max = -1

[Bei Wu]

Hello~

I have been running dropwizard-example to test metrics-jvm module.

I printed out all memory metrics in main() and saw jvm.memory.non-heap.max is set to -1.

and jvm.memory.non-heap.usage is a strange value because -1 is used in its calculations. Is this a known bug to dropwizard dev team?

I can confirm that this happens with metrics-jvm 4.1.17.

Thanks!

[Bei Wu]

Also adding a negative number to the total seems to "pollute" the total  value : https://github.com/dropwizard/metrics/blob/1ca6391043830a03520b98d92bdfeb3a7da4d6b6/metrics-jvm/src/main/java/com/codahale/metrics/jvm/MemoryUsageGaugeSet.java#L48