Exception in IDEA plugin with JDK9

[HaasJona]

Argument for @NotNull parameter 'file' of com/intellij/openapi/roots/impl/ProjectFileIndexImpl.getModuleForFile must not be null
java.lang.IllegalArgumentException: Argument for @NotNull parameter 'file' of com/intellij/openapi/roots/impl/ProjectFileIndexImpl.getModuleForFile must not be null
    at com.intellij.openapi.roots.impl.ProjectFileIndexImpl.getModuleForFile(ProjectFileIndexImpl.java)
    at ch.raffael.doclets.pegdown.integrations.idea.DocCommentProcessor.<init>(DocCommentProcessor.java:101)
    at ch.raffael.doclets.pegdown.integrations.idea.PegdownDocumentationProvider.generateDoc(PegdownDocumentationProvider.java:127)
    at com.intellij.lang.documentation.CompositeDocumentationProvider.generateDoc(CompositeDocumentationProvider.java:144)
    at com.intellij.codeInsight.navigation.CtrlMouseHandler.lambda$null$0(CtrlMouseHandler.java:669)
    at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:855)
    at com.intellij.codeInsight.navigation.CtrlMouseHandler.lambda$fulfillDocInfo$2(CtrlMouseHandler.java:666)
    at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:222)
    at com.intellij.util.Alarm$Request$1.run(Alarm.java:377)
    at com.intellij.util.Alarm$Request.run(Alarm.java:388)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at com.intellij.util.concurrency.SchedulingWrapper$MyScheduledFutureTask.run(SchedulingWrapper.java:227)
    at com.intellij.util.concurrency.BoundedTaskExecutor.runFirstTaskThenPollAndRunRest(BoundedTaskExecutor.java:178)
    at com.intellij.util.concurrency.BoundedTaskExecutor.access$000(BoundedTaskExecutor.java:40)
    at com.intellij.util.concurrency.BoundedTaskExecutor$2.run(BoundedTaskExecutor.java:197)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)