尝试将List <String>添加到HashMap时出现空点异常

我正在尝试将字符串列表添加到HashMap中，我在下面显示了自己的尝试方式。但是我得到了空值异常（我在代码中注释了获得异常的地方）。任何人都可以发现我在犯什么错误。

     private List<Product> mCartList;
     List<String> listDataHeader;
     HashMap<String, List<String>> listDataChild;

        List<String> listdescription = new ArrayList<String>();
        List<String> listcrust = new ArrayList<String>();
        List<String> listsize = new ArrayList<String>();
        String descriptionString;
        String crustString;
        String sizeString;

        for (int i = 0; i < mCartList.size(); i++) {

            mCartList.get(i).selected = false;
            hot_number = mCartList.size();


            if (mCartList.get(i).description != null
                    && !mCartList.get(i).description.isEmpty()) {
                descriptionString = mCartList.get(i).description;

                listdescription.add(descriptionString);
                System.out.println("listdescription = " + listdescription);
            }

            if (mCartList.get(i).crust != null
                    && !mCartList.get(i).crust.isEmpty()) {
                crustString = mCartList.get(i).crust;

                listcrust.add(crustString);
                System.out.println("listcrust = " + listcrust);
            }

            if (mCartList.get(i).size != null
                    && !mCartList.get(i).size.isEmpty()) {
                sizeString = mCartList.get(i).size;

                listsize.add(sizeString);
                System.out.println("listsize = " + listsize);
            }

        }

        listDataChild.put("listcrust", listcrust); // error occurs here
        listDataChild.put("listsize", listsize);

        listDataHeader.addAll(listdescription);

        System.out.println("listDataChild = " + listDataChild);
        System.out.println("listDataHeader = " + listDataHeader);

我已经调试并获得了listsize88行的值，但是当我通过93行时，它给出了下面提到的异常。

异常屏幕截图