Unable to test jenkins plugin class jenkins.plugins.slack.SlackNotifier is missing its descriptor

Question

I make fork from https://github.com/jenkinsci/slack-plugin after add feature I wanna test it, so in intellij idea console i write:

mvn install

And after

mvn hpi:run -Djetty.port=8092

In console i have only information about problem with credentials:

Could not initialize class com.cloudbees.plugins.credentials.SystemCredentialsProvider$UserFa cingAction

But jenkins start. When i try to make build with enable plugin in console I got error:

mar 13, 2018 3:59:31 PM hudson.model.listeners.RunListener report
WARNING: RunListener failed
java.lang.AssertionError: class jenkins.plugins.slack.SlackNotifier is missing its descriptor
        at jenkins.model.Jenkins.getDescriptorOrDie(Jenkins.java:1184)
        at hudson.tasks.Publisher.getDescriptor(Publisher.java:122)
        at hudson.tasks.Notifier.getDescriptor(Notifier.java:51)
        at jenkins.plugins.slack.SlackNotifier.getDescriptor(SlackNotifier.java:69)
        at jenkins.plugins.slack.SlackNotifier.getDescriptor(SlackNotifier.java:40)
        at hudson.model.Descriptor.toMap(Descriptor.java:879)
        at hudson.util.DescribableList.toMap(DescribableList.java:149)
        at jenkins.plugins.slack.SlackListener.getNotifier(SlackListener.java:51)
        at jenkins.plugins.slack.SlackListener.onCompleted(SlackListener.java:27)
        at jenkins.plugins.slack.SlackListener.onCompleted(SlackListener.java:15)
        at hudson.model.listeners.RunListener.fireCompleted(RunListener.java:199)
        at hudson.model.Run.execute(Run.java:1783)
        at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
        at hudson.model.ResourceController.execute(ResourceController.java:98)
        at hudson.model.Executor.run(Executor.java:381)

I completly dont have idea how i can test it from hpi. Anybody have idea?