Do not do this in the constructor, because that will _not_ be called when loading configuration from disk that was saved by an earlier version of the plugin, causing the exception you noticed. Rather use a default value in the `init` method; or create a new method to set up default values for fields, and call from both constructor and `readResolve`. [Wiki](https://wiki.jenkins-ci.org/display/JENKINS/Hint+on+retaining+backward+compatibility)