Kotlin and Gson bug

build.gralde

buildscript {
    ext.kotlin_version = '1.1.4'

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

apply plugin: 'kotlin'

repositories {
    mavenCentral()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
    compile group: 'com.google.code.gson', name: 'gson', version: '2.8.1'
}

ConstructorsInGson.kt

import com.google.gson.Gson

enum class T {A, B}

open class A(val a: T)

class B(val b: T) : A(T.A)

fun main(args: Array<String>) {
    val b = Gson().fromJson("{\"b\":\"B\"}", B::class.java)
    println(b.a) // null
    println(b.b) // B
}