Java.lang.nullpointerexception: attempt to invoke virtual method 'java.lang.string java.lang.object.tostring()' on a null object reference

Process: id.ac.astra.polytechnic.toolmaintenance, PID: 22120
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
    at id.ac.astra.polytechnic.toolmaintenance.viewModel.RoleListViewModel.addRole(RoleListViewModel.java:53)
    at id.ac.astra.polytechnic.toolmaintenance.AddRoleFragment$2.onClick(AddRoleFragment.java:79)
    at android.view.View.performClick(View.java:7756)
    at android.view.View.performClickInternal(View.java:7729)
    at android.view.View.access$3700(View.java:860)
    at android.view.View$PerformClick.run(View.java:29318)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loopOnce(Looper.java:210)
    at android.os.Looper.loop(Looper.java:299)
    at android.app.ActivityThread.main(ActivityThread.java:8298)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:576)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1073)

public class AddRoleFragment extends Fragment {
    private Role mRole;
    private EditText roleName;
    private RoleListViewModel mRoleListViewModel;


    public static AddRoleFragment newInstance() {
        return new AddRoleFragment();
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        Log.i(TAG, "UserFragment.onCreate() called");

        mRole = new Role();
        mRoleListViewModel = new ViewModelProvider(this)
                .get(RoleListViewModel.class);

    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.add_role, container, false);

        Button btnSimpan = view.findViewById(R.id.btnSimpan);
        roleName = view.findViewById(R.id.inputNamaJabatan);
        roleName.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int i, int i1, int i2) {

            }

            @Override
            public void onTextChanged(CharSequence s, int i, int i1, int i2) {
               mRole.setRolename(s.toString());
            }

            @Override
            public void afterTextChanged(Editable editable) {

            }
        });
        btnSimpan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Ketika btnPeminjaman ditekan, tampilkan PeminjamanFragment

            //    mRole.setRolename(String.valueOf(roleName));

                mRoleListViewModel.addRole(mRole);

                Fragment peminjamanFragment = ListKelolaRoleFragment.newInstance();
                FragmentManager fragmentManager = getFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.fragment_container, peminjamanFragment, "peminjaman");
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
            }
        });

        return view;
    }
}

public class RoleListViewModel extends ViewModel {

    private MutableLiveData<List<Role>> mRoleListMutableLiveData;
    private RoleRepository mRoleRepository;

    public RoleListViewModel(){
        Log.d(TAG, "RoleListViewModel constructor called");
        mRoleRepository = RoleRepository.get();

    }
    public MutableLiveData<List<Role>> Roles(){
        mRoleListMutableLiveData = mRoleRepository.Roles();
        Log.d(TAG,"RoleListViewModel.getRoles() called ="+
                mRoleListMutableLiveData.toString());
        return mRoleListMutableLiveData;
    }

    public void addRole (Role Role) {

        mRoleRepository.addRole (Role);
        Log.d(TAG,"RoleListViewModel.getRoles() called ="+
                mRoleListMutableLiveData.toString());
    }
    }

public class RoleRepository {
    private static final String TAG = "RoleRepository";
    public static RoleRepository INSTANCE;

    private RoleService mRoleService;

    private MutableLiveData<List<Role>> mRoleListMutableLiveData;

    //hubungan dgn APIutils utk daepetin fungsi
    private RoleRepository(Context context) {
        mRoleService = ApiUtils.getRoleService();
    }

    public static void initialize(Context context) {
        if (INSTANCE == null) {
            INSTANCE = new RoleRepository(context);
        }
    }
    private  RoleRepository(){

    }
    public static RoleRepository get() {

        return INSTANCE;
    }

    public MutableLiveData<List<Role>> Roles() {
        MutableLiveData<List<Role>> Roles = new MutableLiveData<List<Role>>();

        Call<List<Role>> call = mRoleService.Roles();
        call.enqueue(new Callback<List<Role>>() {
            @Override
            public void onResponse(Call<List<Role>> call, Response<List<Role>> response) {
                if (response.isSuccessful()) {
                    Roles.setValue(response.body());
                    Log.d(TAG, "getRoles.onResponse() called");
                }
            }

            @Override
            public void onFailure(Call<List<Role>> call, Throwable t) {
                Log.e("Error API call :", t.getMessage());
            }
        });
        return Roles;
    }

    public void addRole(Role Role){
        Log.i(TAG, "addRole() called");
        Call <Role> call = mRoleService.addRole (Role);
        Log.i(TAG, "addRole2() called");

        call.enqueue(new Callback<Role>() {
            @Override
            public void onResponse (Call<Role> call, Response <Role> response) { if (response.isSuccessful()){
                Log.i(TAG, "Role added " + Role.getRolename());
            }
            }
            @Override
            public void onFailure (Call<Role> call, Throwable t) {
                Log.e("Error API call ", t.getMessage());
            }
        });
    }
}