hudson.tasks.BuildTrigger#getChildProjects(hudson.model.ItemGroup) doesn't check if childProjects is null.

Even though childProjects is checked for null in the constructor, this can happen if a BuildTrigger is deserialized from an invalid configuration.

What's worse, is that due to JENKINS-26643, this can prevent Jenkins from starting. Example:

SEVERE: Failed Finalizing set up
java.lang.NullPointerException
at java.util.StringTokenizer.<init>(Unknown Source)
at java.util.StringTokenizer.<init>(Unknown Source)
at hudson.model.Items.fromNameList(Items.java:145)
at hudson.plugins.parameterizedtrigger.BuildTriggerConfig.getProjectList(BuildTriggerConfig.java:125)
at hudson.plugins.parameterizedtrigger.BuildTrigger.buildDependencyGraph(BuildTrigger.java:74)
at hudson.util.DescribableList.buildDependencyGraph(DescribableList.java:213)
at hudson.model.Project.buildDependencyGraph(Project.java:201)
at hudson.model.DependencyGraph.build(DependencyGraph.java:95)
at jenkins.model.Jenkins.rebuildDependencyGraph(Jenkins.java:3738)
at jenkins.model.Jenkins$20.run(Jenkins.java:2680)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:886)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)