NotNull delegate with lazy message

NotNull.kt

fun <T: Any> notNull(lazyMessage: () -> Any): ReadWriteProperty<Any?, T> = NotNullVar(lazyMessage)

private class NotNullVar<T: Any>(val lazyMessage: () -> Any)  : ReadWriteProperty<Any?, T> {
    private var value: T? = null

    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return value ?: throw IllegalStateException(lazyMessage.toString())
    }

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        this.value = value
    }
}