Android LiveData Resource: Propagate Data or Exception (Kotlin)

class Resource<out T> private constructor(    private val data: T?,    private val error: Throwable?) {    val isSuccessful: Boolean        get() = data != null && error == null    constructor(data: T) : this(data, null)    constructor(exception: Throwable) : this(null, exception)    fun data(): T {        if (error != null) {            throw IllegalStateException("Check isSuccessful first: call error() instead.")        }        return data!!    }    fun error(): Throwable {        if (data != null) {            throw IllegalStateException("Check isSuccessful first: call data() instead.")        }        return error!!    }}

val messageLiveData = MutableLiveData<Resource<String>>()

fun getMessage() {    try {        // fetch data        val message = ...        messageLiveData.value = Resource(message)    }    catch (e: Exception) {        messageLiveData.value = Resource(e)    }}

messageLiveData.observe(lifecycleOwner, Observer { event ->    if (event.isSuccessful) {        val message = res.data()        // do something    }    else {        val e = res.error()        // handle exception    }}