[TRI-3566] Logging strips out key/value pairs when the value is `0`

[matt-aitken]

If you do this:

logger.log("Some text", { foo: "bar", val: 0 });

The properties that are stored are just:

{ "foo": "bar" }

It should include "val": 0 as well. This is most likely a bug when we flatten the attributes into a flat structure. A classic falsy check bug is my guess.

_TRI-3566

[abhi12299]

@matt-aitken how do i reproduce the issue? this is working fine: