How can I make the LiveData getValue() function return the list of items from my rooms database in Android?

I have a getAllFlights() method in my ViewModel class which is supposed to return all the flights in my rooms database, however, when I call the method in my activity, it returns null even though I have flights existing in the database. Below is the code for my activity where I am calling flightViewModel.getAllFlights.getValue() method. I am using the MVVM model.

Activity code

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_report_listing);

        uploadAllBtn = findViewById(R.id.uploadAllReports);
        searchFlights = findViewById(R.id.searchFlightText);
        mRecyclerView = findViewById(R.id.recyclerView);


        flightViewModel = new ViewModelProvider(this).get(FlightViewModel.class);

        flightViewModel.getAllFlights().observe(this, new Observer<List<Flight>>() {
            @Override
            public void onChanged(List<Flight> flight_list) {

                String flightno = flight_list.get(1).getFlightNumber();
                String flightdate = flight_list.get(1).getDate();

                String[] flight_details = new String[2];
                flight_details[0]= flightno;
                flight_details[1] = flightdate;

                Log.v("pp", flight_details[0]);

                for(int i = 0; i <flight_list.size();i++){
                    String flightnumber = flight_list.get(i).getFlightNumber();
                    String departuredate = flight_list.get(i).getDate();

                    reportitems.add(new ReportItem(flightnumber,departuredate));

                    
                }
                flightViewModel.getAllFlights().removeObservers(ReportListingActivity.this);
            }
        });

        mLayoutManager = new LinearLayoutManager(ReportListingActivity.this);
        mAdapter = new ReportAdapter(reportitems, ReportListingActivity.this);

        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setAdapter(mAdapter);
    }