The optional plugin doesn't work well with kotlin gradle scripts.

In JAVA-5239 I added an optional dependency but can't mark it as optional with the current plugin.

See: https://blog.gradle.org/optional-dependencies

Using "features" optional feature dependencies can be declared eg:

java {
    registerFeature("jsonSupport") {
        usingSourceSet(sourceSets["main"])
    }
}

Then used like so:

dependencies {
    "jsonSupportImplementation"("org.jetbrains.kotlinx:kotlinx-serialization-json")
}