java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getImportantForAccessibility()' on a null object reference

In your public View getView method change return null; to return convertView;.

#use return convertView;

Code:

public View getView(final int position, View convertView, ViewGroup parent) {

    //convertView = null;

    if (convertView == null) {

        LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        convertView = mInflater.inflate(R.layout.list_item, null);     

        TextView tv = (TextView) convertView.findViewById(R.id.name);
        Button rm_btn = (Button) convertView.findViewById(R.id.rm_btn);

        Model m = modelList.get(position);
        tv.setText(m.getName());

        // click listener for remove button  คลิกลบปุ่ม
        rm_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                modelList.remove(position);
                notifyDataSetChanged();
            }
        });
    }

    ///#use    return convertView;
    return convertView;
}

in your baseadapter class constructor try to initialize LayoutInflater, normally i preferred this way,

public ClassBaseAdapter(Context context,ArrayList<Integer> listLoanAmount) {
    this.context = context;
    this.listLoanAmount = listLoanAmount;
    this.layoutInflater = LayoutInflater.from(context);
}

at the top of the class create LayoutInflater variable, hope this will help you