A user added a multijob step to a job (I think clicking the Advanced button, checking Current job parameters and Exposed SCM) and tried to save it and got an error:

javax.servlet.ServletException: java.lang.NoClassDefFoundError: hudson/plugins/parameterizedtrigger/AbstractBuildParameters$DontTriggerException

This was solved only by installing the Parameterized Trigger plugin (2.17). If that dependency is needed to avoid linkage errors when saving job configuration at least under some circumstances, then I think it should be a mandatory, not optional, dependency.