Pixplicity's

class AbsentLiveData<T : Any?> private constructor() : LiveData<T>() {
    init {
        // use post instead of set since this can be created on any thread
        postValue(null)
    }

    companion object {
        fun <T> create(): LiveData<T> {
            return AbsentLiveData()
        }
    }
}

val someLiveData: LiveData<Any> =
        Transformations.switchMap(myTrigger) {
            if (it != null) {
                repository.getSomeLiveData()
            } else {
                AbsentLiveData.create()
            }
        }