Why does custom spinner throw NotFoundException?

Question

Android

There is a custom spinner:

public class CustomSpinner extends AppCompatSpinner {
    public interface OnSpinnerEventsListener {
        void onPopupWindowOpened(Spinner spinner);
        void onPopupWindowClosed(Spinner spinner);
    }

    private OnSpinnerEventsListener mListener;
    private boolean mOpenInitiated = false;

    public CustomSpinner(Context context) {
        super(context);
    }

    public CustomSpinner(@NonNull Context context, int mode) {
        super(context, mode);
    }

    public CustomSpinner(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomSpinner(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public CustomSpinner(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr, int mode) {
        super(context, attrs, defStyleAttr, mode);
    }

    public CustomSpinner(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr, int mode, Resources.Theme popupTheme) {
        super(context, attrs, defStyleAttr, mode, popupTheme);
    }

    @Override
    public boolean performClick() {
        mOpenInitiated = true;
        if (mListener != null) {
            mListener.onPopupWindowOpened(this);
        }
        return super.performClick();
    }

    @Override
    public void onWindowFocusChanged (boolean hasFocus) {
        if (hasBeenOpened() && hasFocus) {
            performClosedEvent();
        }
    }

    /**
     * Register the listener which will listen for events.
     */
    public void setSpinnerEventsListener(
            OnSpinnerEventsListener onSpinnerEventsListener) {
        mListener = onSpinnerEventsListener;
    }

    /**
     * Propagate the closed Spinner event to the listener from outside if needed.
     */
    public void performClosedEvent() {
        mOpenInitiated = false;
        if (mListener != null) {
            mListener.onPopupWindowClosed(this);
        }
    }

    /**
     * A boolean flag indicating that the Spinner triggered an open event.
     *
     * @return true for opened Spinner
     */
    public boolean hasBeenOpened() {
        return mOpenInitiated;
    }

}

And an adapter for it:

public class SpinnerAdapter extends ArrayAdapter<String> {

    Context ctx;
    String[] contentArray;
    Integer[] imageArray;

    public SpinnerAdapter(Context context, int resource, String[] objects, Integer[] imageArray) {
        super(context, R.layout.drop_list_item, R.id.spinnerTextView, objects);
        this.ctx = context;
        this.contentArray = objects;
        this.imageArray = imageArray;
    }

    @Override
    public View getDropDownView(int position, View convertView, @NonNull ViewGroup parent) {
        return getCustomView(position, convertView, parent);
    }

    @Override
    public View getView(int position, View convertView, @NonNull ViewGroup parent) {
        return getCustomView(position, convertView, parent);
    }

    public View getCustomView(int position, View convertView, ViewGroup parent) {

        LayoutInflater inflater = (LayoutInflater)ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View row = inflater.inflate(R.layout.drop_list_item, parent, false);

        TextView textView = (TextView) row.findViewById(R.id.spinnerTextView);
        textView.setText(contentArray[position]);

        ImageView imageView = (ImageView)row.findViewById(R.id.spinnerImages);
        imageView.setImageResource(imageArray[position]);

        return row;
    }
}

In activity:

String[] textArray = {"Choose Lang", "Russian", "English", "Czech"};
    Integer[] imageArray = {R.mipmap.lang_ru_round, R.mipmap.lang_ru_round, R.mipmap.lang_en_round, R.mipmap.lang_cs_round};

SpinnerAdapter spinnerAdapter = new SpinnerAdapter(this, R.layout.drop_list_item, textArray, imageArray);
        spinner.setAdapter(spinnerAdapter);
        spinner.setSpinnerEventsListener(this);
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {

                if (parentView.getItemAtPosition(position).equals("Choose Lang")) {
                    //do nothing.
                } else {
                    if (spinner.getSelectedItem().toString().equals("Russian")) {
                        lang.updateResource("ru");
                        Intent intent = getIntent();
                        finish();
                        startActivity(intent);
                    } else if (spinner.getSelectedItem().toString().equals("English")) {
                        lang.updateResource("en");
                        Intent intent = getIntent();
                        finish();
                        startActivity(intent);
                    } else if (spinner.getSelectedItem().toString().equals("Czech")) {
                        lang.updateResource("cs");
                        Intent intent = getIntent();
                        finish();
                        startActivity(intent);
                    }
                }
            }

            @Override
            public void onNothingSelected(AdapterView<?> parentView) {

            }

        });

@Override
    public void onPopupWindowOpened(Spinner spinner) {
        spinner.setBackground(getResources().getDrawable(R.drawable.drop_list_up));
    }

    @Override
    public void onPopupWindowClosed(Spinner spinner) {
        spinner.setBackground(getResources().getDrawable(R.drawable.drop_list));
    }

When clicking on the spinner, it gives an error:

android.content.res.Resources$NotFoundException: Resource ID #0x7f08006c
  at android.content.res.Resources.getValue(Resources.java:1369)
  at android.content.res.MiuiResources.getValue(MiuiResources.java:147)
  at android.content.res.Resources.getDrawable(Resources.java:822)
  at android.content.res.Resources.getDrawable(Resources.java:789)
  at abox.org.aboxopen.BoxesActivity.onPopupWindowOpened(BoxesActivity.java:198)
  at abox.org.aboxopen.CustomSpinner.performClick(CustomSpinner.java:48)
  at android.view.View$PerformClick.run(View.java:21196)
  at android.os.Handler.handleCallback(Handler.java:742)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:157)
  at android.app.ActivityThread.main(ActivityThread.java:5603)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:774)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)

Crashes on Android 6 version, above everything works.
What is the problem and how to solve it?