[JENKINS-15156] Found a problem with uninitialized run maps in new Maven modules.

Not observed in actual usage, but reproducible (for me at least, though apparently not ci.jenkins-ci.org) in a test:
java.lang.AssertionError: null
    at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:628)
    at jenkins.model.lazy.AbstractLazyLoadRunMap.all(AbstractLazyLoadRunMap.java:581)
    at jenkins.model.lazy.AbstractLazyLoadRunMap.entrySet(AbstractLazyLoadRunMap.java:243)
    at java.util.AbstractMap$2$1.<init>(AbstractMap.java:378)
    at java.util.AbstractMap$2.iterator(AbstractMap.java:377)
    at hudson.util.RunList.iterator(RunList.java:103)
    at hudson.util.RunList.size(RunList.java:114)
    at hudson.maven.MavenProjectTest.testDeleteSetBuildDeletesModuleBuilds(MavenProjectTest.java:159)