Clear values inside of the MutableLiveData response collection

I have an app, which uses api calls, to get some data by Retrofit from the server. I've implemented SwiperRefreshLayout to allow user, to perform another call.

Currently, I'm struggling with clearing MutableLiveData collection, which stores response from the server. I'd like to clear that collection every time the OnRefreshListener will be triggered.

I've tried to "fill" the MutableLiveData with null (as it comes by default, right?) but since I've set the observable in OnCreateView to pass the data to the Adapter, after every refresh I got NullPointerException error.

How I may solve it? Should I do something like unobserving, and observing the response collection again, when OnRefreshListener is triggered? Here's some code:

ViewModel

var responseData = MutableLiveData<Model?>()



fun fetchData(baseCurrency: String, selectedCurrencies: String) {
    viewModelScope.launch {
        val response =
            retrofitRepository.fetchHistoricalData(date, selectedCurrencies, baseCurrency)
        response.enqueue(object : retrofit2.Callback<Model> {
            override fun onResponse(
                call: Call<HistoricalRatesModel>,
                response: Response<HistoricalRatesModel>
            ) {
                if (response.isSuccessful) {
                    responseData.value = response.body()
                }
            }

            override fun onFailure(call: Call<HistoricalRatesModel>, t: Throwable) {
                Log.i(TAG, "onFailure ERROR\n${t.message}")
            }
        })
    }
}

Fragment

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        _binding = FragmentHistoricalRatesBinding.inflate(inflater, container, false)
        val view = mBinding.root

      
        mViewModel.responseData.observe(requireActivity(), androidx.lifecycle.Observer {
            mAdapter = Adapter()
            mAdapter?.setData(it!!.rates)
            mBinding.hrv.layoutManager = LinearLayoutManager(this.context)
            mBinding.hrv.adapter = mAdapter
        })

        mBinding.refreshContainer.setOnRefreshListener {
            mBinding.refreshContainer.isRefreshing = false
        }
        return view
}

You're not handling that potential null value in your observer - in fact you're telling the compiler that it will never be null!

mViewModel.responseData.observe(requireActivity(), androidx.lifecycle.Observer {
    ...
    mAdapter?.setData(it!!.rates)
})

How you handle it depends on what you want to do when that null value is pushed to observers. If you want to clear the data in the adapter, you could do:

mAdapter?.setData(it?.rates ?: emptyList<Rate>())

or you could make your Adapter's setData() function accept null (and decide internally how to handle that) and then you can just do:

mAdapter?.setData(it?.rates)

If any of that's confusing, make sure you're familiar with the null safety features in Kotlin, and how thing?.stuff?.value evaluates to null if any of those variables in the chain are null