Log4s/log4s — pull request #2 by dyross (2014-08-18 04:57:44+00:00)
Title: Handle `null`s returned by `getCopyOfContextMap`.

`getCopyOfContextMap` returns `null` for empty `MDC`s:

http://www.slf4j.org/api/org/slf4j/MDC.html#getCopyOfContextMap()

Do we want the returned copy map to be mutable or not?