jenkinsci/jenkins — pull request #897 by lvotypko (2013-08-05 11:17:48+00:00)
Title: Fix NullPointerException which is possible in concurrent builds.

If there is enabled concurrent builds and build 1 is in progress and build 2 is finished, artifact archiver throw NullPointerException for build 3.

I replaced HudsonTestCase with JenkinsRule when I write test for this behaviour.