Why do I get java.lang.IllegalArgumentException when I call setUp from LightPlatformCodeInsightTestCase

I want to test my KotlinParser. It extends the class KotlinRecursiveElementWalkingVisitor. So in order to test the class I have to create a mock PsiFile. I tried to use the LightPlatformCodeInsightTestCase class which provides the createLightFile method. So I implemented the following test class:

import com.intellij.testFramework.LightPlatformCodeInsightTestCase
import org.apache.commons.io.IOUtils
import org.junit.jupiter.api.Test
import java.io.File
import java.io.FileInputStream

class PluginCeckerTest : LightPlatformCodeInsightTestCase() {

    @Test
    fun checkTestBuildFile1_kotlin() {
        super.setUp()
        val parser = KotlinParser()
        val testFile = File("src/test/resources/test_build_scripts/testbuild1.gradle.kts")
        val filecontent = IOUtils.toString( FileInputStream(testFile), "UTF-8")
        val psifile = createLightFile("test.gradle.kts", filecontent)
        if (psifile != null) {
            parser.visitFile(psifile)
        }
    }
}

I already checked with println that the code fails during super.setUp().

This is the error that I get:

java.lang.IllegalArgumentException: Argument for @NotNull parameter 's' of com/intellij/openapi/util/text/StringUtil.trimStart must not be null
    at com.intellij.openapi.util.text.StringUtil.$$$reportNull$$$0(StringUtil.java)
    at com.intellij.openapi.util.text.StringUtil.trimStart(StringUtil.java)
    at com.intellij.testFramework.LightPlatformTestCase.getTestName(LightPlatformTestCase.java:552)
    at com.intellij.testFramework.UsefulTestCase.createGlobalTempDirectory(UsefulTestCase.java:254)
    at com.intellij.testFramework.UsefulTestCase.setupTempDir(UsefulTestCase.java:242)
    at com.intellij.testFramework.UsefulTestCase.setUp(UsefulTestCase.java:214)
    at com.intellij.testFramework.LightPlatformTestCase.lambda$setUp$2(LightPlatformTestCase.java:222)
    at com.intellij.testFramework.EdtTestUtil.lambda$runInEdtAndWait$1(EdtTestUtil.java:40)
    at com.intellij.openapi.application.TransactionGuardImpl.runWithWritingAllowed(TransactionGuardImpl.java:209)
    at com.intellij.openapi.application.TransactionGuardImpl.access$100(TransactionGuardImpl.java:21)
    at com.intellij.openapi.application.TransactionGuardImpl$1.run(TransactionGuardImpl.java:191)
    at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:831)
    at com.intellij.openapi.application.impl.ApplicationImpl$3.run(ApplicationImpl.java:456)
    at com.intellij.openapi.application.impl.LaterInvocator$1.run(LaterInvocator.java:101)
    at com.intellij.openapi.application.impl.FlushQueue.doRun(FlushQueue.java:79)
    at com.intellij.openapi.application.impl.FlushQueue.runNextEvent(FlushQueue.java:122)
    at com.intellij.openapi.application.impl.FlushQueue.flushNow(FlushQueue.java:41)
    at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:318)
    at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:788)
    at java.desktop/java.awt.EventQueue$3.run(EventQueue.java:739)
    at java.desktop/java.awt.EventQueue$3.run(EventQueue.java:731)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:758)
    at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.kt:667)
    at com.intellij.ide.IdeEventQueue._dispatchEvent$lambda$7(IdeEventQueue.kt:571)
    at com.intellij.openapi.application.impl.ApplicationImpl.withoutImplicitRead(ApplicationImpl.java:1446)
    at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.kt:571)
    at com.intellij.ide.IdeEventQueue.access$_dispatchEvent(IdeEventQueue.kt:68)
    at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1$1.compute(IdeEventQueue.kt:349)
    at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1$1.compute(IdeEventQueue.kt:348)
    at com.intellij.openapi.progress.impl.CoreProgressManager.computePrioritized(CoreProgressManager.java:787)
    at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1.invoke(IdeEventQueue.kt:348)
    at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1.invoke(IdeEventQueue.kt:343)
    at com.intellij.ide.IdeEventQueueKt.performActivity$lambda$1(IdeEventQueue.kt:995)
    at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:105)
    at com.intellij.ide.IdeEventQueueKt.performActivity(IdeEventQueue.kt:995)
    at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$4(IdeEventQueue.kt:343)
    at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:831)
    at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.kt:385)
    at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:207)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
    at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:92)

 

I don't know how to resolve this error. In case you need further information I will be happy to provide it.

Thanks in advance for your help!