When starting a kotlin tornadofx project, I get Error running 'MainView'?

Question

IntelliJ IDEA

I am new to kotlin. In Intellij Idea, I tried to create a standard project with the TornadoFX plugin, at first Hello World started, but the next day an error appeared:

Error running 'MainView': Argument for @NotNull parameter 'mainClassName' of com/intellij/execution/util/JavaParametersUtil.isClassInProductionSources must not be null

Help me understand what is the problem, where is my mainClassName equal to zero? And why didn't this error appear immediately. Thanks in advance!

MainView.kt

package com.example.demo.view

import com.example.demo.app.Styles
import tornadofx.*

class MainView : View("Hello Tornado") {
    override val root = hbox {
        label(title) {
            addClass(Styles.heading)
        }
    }
}

build.gradle

buildscript {
    ext.kotlin_version = '1.2.51'

    repositories {
        mavenLocal()
        mavenCentral()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

apply plugin: "kotlin"
apply plugin: 'application'

compileKotlin {
    kotlinOptions.jvmTarget = "1.8"
}

repositories {
    mavenLocal()
    mavenCentral()
    maven {
        url "https://oss.sonatype.org/content/repositories/snapshots/"
    }
}

dependencies {
    compile 'no.tornado:tornadofx:1.7.14'
    testCompile 'junit:junit:4.12'
    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
}

mainClassName = 'com.example.demo.app.MyApp'

jar {
    manifest {
        attributes(
                'Class-Path': configurations.compile.collect { it.getName() }.join(' '),
                'Main-Class': 'com.example.demo.app.MyApp'
        )
    }
    from(configurations.compile.collect { entry -> zipTree(entry) }) {
        exclude 'META-INF/MANIFEST.MF'
        exclude 'META-INF/*.SF'
        exclude 'META-INF/*.DSA'
        exclude 'META-INF/*.RSA'
    }
}

MyView.kt

package com.example.demo.view

import tornadofx.*

class MyView : View("My View") {
    override val root = borderpane {

    }
}

MyApp.kt

package com.example.demo.app

import com.example.demo.view.MainView
import tornadofx.App

class MyApp: App(MainView::class, Styles::class)

Styles.kt

package com.example.demo.app

import javafx.scene.text.FontWeight
import tornadofx.Stylesheet
import tornadofx.box
import tornadofx.cssclass
import tornadofx.px

class Styles : Stylesheet() {
    companion object {
        val heading by cssclass()
    }

    init {
        label and heading {
            padding = box(100.px)
            fontSize = 20.px
            fontWeight = FontWeight.BOLD

        }
    }
}

Answer 1

Put java Liberica, there is a built-in javafx