Merge pull request #36 from waltflanagan/master

[FIXED JENKINS-20037]
[maven-release-plugin] prepare release xcode-plugin-1.4.1
[maven-release-plugin] prepare for next development iteration
Avoid NPE on plugin version update

When upgrading from 1.3 to 1.4.x, this configuration key does not yet
exist, causing every XCode build to break. Added  a null check to avoid
this situation. [JENKINS-19886]
Merge pull request #37 from vzsg/master

Avoid NPE on plugin version update