CatModel!

MainViewModel.kt

class MainViewModel : ViewModel() {

    private val compositeDisposableOnDestroy = CompositeDisposable()
    private var latestCatCall: Disposable? = null
    // the list that will be observed by the activity
    val bunchOfCats = MutableLiveData<List<NetCat>>()
    // the error message observed
    val errorMessage = MutableLiveData<String>()

    // the API call
    fun getSomeCats() {
        // initialising the repository class with the necessary information
        val catsRepository = CatsRepository(serverUrl, BuildConfig.DEBUG, apiKey)

        // stopping the last call if it's already running (optional)
        latestCatCall?.dispose()

        // perform the API call
        // asking for 10 cats. Don't care in what category so just passing null
        latestCatCall =
            catsRepository.getNumberOfRandomCats(10, null).subscribeOn(Schedulers.io())
                .doOnSubscribe {
                    compositeDisposableOnDestroy.add(it)
                }
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe { result ->
                    when {
                        result.hasError() -> result.errorMessage?.let {
                            // anyone who observes this will be notified of the change automatically
                            errorMessage.postValue("Error getting cats $it")
                        }
                            ?: run {
                                // anyone who observes this will be notified of the change automatically
                                errorMessage.postValue("Null error :(")
                            }
                        result.hasCats() -> result.netCats?.let {
                            // anyone who observes this will be notified of the change automatically
                            bunchOfCats.postValue(it)
                            // clearing the error if it existed (hacky and optional)
                            errorMessage.postValue("")
                        }
                            ?: run {
                                // anyone who observes this will be notified of the change automatically
                                errorMessage.postValue("Null list of cats :(")
                            }
                        else -> {
                            // anyone who observes this will be notified of the change automatically
                            errorMessage.postValue("No cats available :(")
                        }
                    }
                }
    }

    // clearing the collection of disposables = no memory leaks no matter what
    override fun onCleared() {
        compositeDisposableOnDestroy.clear()
        Log.d("TAG", "Clearing ViewModel")
        super.onCleared()
    }
}

Hey, thanks for the kind words :)
You can find the CatsRepository class here.
In the constructor it has these 3 fields declared (lines 5,6 and 7).
The latestCatCall: Disposable variable is a var (on line 4 of this file). So it can be changed at any time.