How to create a task to run an application using Gradle Kotlin DSL?

Question

gradle

Good afternoon.
Decided to try Gradle Kotlin DLS.
I have a program with several entry points, and to run them, I made separate tasks of the form:

task runMain(type: JavaExec) {
    classpath = sourceSets.main.runtimeClasspath
    main = "ru.mipt.npm.mcengine.MainKt"
    standardInput = System.in
}

Now I am trying to do like this:

tasks.create<JavaExec>("runMain"){
    classpath = java.sourceSets["main"].runtimeClasspath
    main = "ru.mipt.npm.mcengine.MainKt"
    standardInput = System.`in`
}

However, there is some problem with the classpath, it doesn't work with an error:

Script compilation error:

  Line 38:     classpath = java.sourceSets["main"].runtimeClasspath
                                ^ Unresolved reference. None of the following candidates is applicable because of receiver type mismatch: 
                                    public val Project.sourceSets: SourceSetContainer defined in org.gradle.kotlin.dsl

What to do? Studying the documentation did not lead me to an answer.
PS I know about the application plugin, it does not suit me.