If a job inside a multijob phase is disabled, I see an error and NPE:

Starting build job core-8_0-func_fast_functional-develop.
Starting build job core-8_0-func_bats-develop.
Starting build job core-8_0-unit_test-develop.

((( core-8_0-unit_test-develop is disabled )))

Warning: can't execute one of core-8_0-unit_test-develop builds, due to jenkins limitations.Starting build job core-8_0-func_fast_functional_content-develop.

FATAL: null
java.lang.NullPointerException
at com.tikal.jenkins.plugins.multijob.MultiJobBuilder.perform(MultiJobBuilder.java:121)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:780)
at hudson.model.Build$BuildExecution.build(Build.java:199)
at hudson.model.Build$BuildExecution.doRun(Build.java:160)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:565)
at com.tikal.jenkins.plugins.multijob.MultiJobBuild$MultiJobRunnerImpl.run(MultiJobBuild.java:70)
at hudson.model.Run.execute(Run.java:1592)
at hudson.model.Run.run(Run.java:1539)
at com.tikal.jenkins.plugins.multijob.MultiJobBuild.run(MultiJobBuild.java:63)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:237)

Correct behavior, I believe, would be to ignore the job.

Workaround is to remove the job from the multijob configuration.