[FIXED JENKINS-20166] Promoted Build NullPointer when not manual promotion
Ensuring it is possible to test this plugin against newer Jenkins cores using plugin-compat-tester.
Special care must be taken with Guava, of which various versions are floating around, some of which are not backward compatible.
Merge pull request #33 from cvarjao/JENKINS-20166

[FIXED JENKINS-20166] Promoted Build NullPointer when not manual promoti...
[maven-release-plugin] prepare release promoted-builds-2.15
[maven-release-plugin] prepare for next development iteration