NPE if service is missing from dimensions

[matthayter]

This line throws an NPE if the service key is missing from dimensions.

In general, should the code assume that certain dimensions are present (service, host, cluster) and therefore verify this upon parsing; or should the code make no assumptions about present dimensions?

I believe the latter, but just wanted to confirm, as the above line appears to be @vjkoskela 's change.

[vjkoskela]

So the reason to expose these "special" dimensions was because we have and likely will need to continue to have logic based on them. However, there seems to be a miss when they are not present. Either, the code should wrap those special dimensions with Optional or default the value (e.g. to "" or "DEFAULT_SERVICE").

I don't think we should require them to be there are the parser level. I'm partial to an incremental solution where we call a duck a duck; that is, mark those accessors as Optional. @BrandonArp do you have a preference on how we expand this logic?