Multi-module project, using buildSrc and Kotlin script for build.

Change kotlin version from 1.5.20 to 1.6.0 or 1.6.10 cause:

org.gradle.internal.exceptions.LocationAwareException: Build file '/projectpath/library/build.gradle.kts' line: 1
at Program.execute(Unknown Source)
    at org.gradle.kotlin.dsl.execution.Interpreter$ProgramHost.eval(Interpreter.kt:506)
    at org.gradle.kotlin.dsl.execution.Interpreter.eval(Interpreter.kt:200)

build.gradle.kts of buildSrc:

repositories {
    // so that external plugins can be resolved in dependencies section
    gradlePluginPortal()
    mavenCentral()
}

plugins {
    `kotlin-dsl`
}

dependencies {
    // We need these dependencies to be able to use customized `org.openapitools.generator.gradle.plugin.tasks.GenerateTask`
    // in `xxx_api_generator.gradle`, e.g. `bootstrap_api_generator.gradle`.
    runtimeOnly("org.openapitools:openapi-generator-gradle-plugin:5.1.1")
    runtimeOnly("com.google.guava:guava:30.1.1-jre")
    runtimeOnly("io.gitlab.arturbosch.detekt:detekt-gradle-plugin:1.18.0-RC2")
}

Any Ideas?