解析JSON字符串时出现空指针异常错误

Question

JSON String是这样的：

{
    "products": [{
        "Variants": [{
            "SellPrice": "18.00",
            "VariantID": "1",
            "VariantName": "50 GM",
            "InCart": "0",
            "MRP": "19.00",
            "VariantImagePath": null
        }],
        "SubCategoryID": "44",
        "ProductImagePath": "/images/patanjali/1819.png",
        "SubCategoryName": "Bathing Soap",
        "BrandName": "Patanjali",
        "ProductID": "1",
        "BrandID": "112",
        "ProductName": "Body Cleanser - Lemon Honey Kanti"
    }, {
        "Variants": [{
            "SellPrice": "24.00",
            "VariantID": "47",
            "VariantName": "75 GM",
            "InCart": "0",
            "MRP": "25.00",
            "VariantImagePath": null
        }],
        "SubCategoryID": "44",
        "ProductImagePath": "/images/patanjali/1817.png",
        "SubCategoryName": "Bathing Soap",
        "BrandName": "Patanjali",
        "ProductID": "2",
        "BrandID": "112",
        "ProductName": "Body Cleanser - Mogra"
    }]
} 

这个用于解析字符串的逻辑。

try {
    JSONObject jsonRootObject = new JSONObject(jsonStr);
    //Get the instance of JSONArray that contains JSONObjects
    JSONArray jsonArray = jsonRootObject.optJSONArray("products");
    //Iterate the jsonArray and print the info of JSONObjects
    //utility.displayToast(jsonArray.length() + " ");
    for (int i = 0; i < jsonArray.length(); ++i) {
        JSONObject jsonObject = jsonArray.getJSONObject(i);
        int id = Integer.parseInt(jsonObject.optString("ProductID").toString());
        String name = jsonObject.optString("ProductName").toString();
        String imagePath = Utility.BASEURL + jsonObject.optString("ProductImagePath").toString();

        int brandId = Integer.parseInt(jsonObject.optString("BrandID").toString());
        String brandName = jsonObject.optString("BrandName").toString();

        Brand b = new Brand(brandId, brandName, null);

        JSONArray variantArray = jsonRootObject.optJSONArray("Variants");
        ArrayList <ProductVariant> productVariant = new ArrayList<>();
        for (int j = 0; j < variantArray.length(); ++j){
            JSONObject variantObject = variantArray.getJSONObject(j);
            int variantId = Integer.parseInt(variantObject.optString("VariantID").toString());
            String variantName = variantObject.optString("VariantName");
            Double variantMRP = Double.parseDouble(variantObject.optString("MRP").toString());
            Double variantSellPrice = Double.parseDouble(variantObject.optString("SellPrice").toString());
            Variant variant = new Variant(variantId, variantName);
            ProductVariant pVariant = new ProductVariant(0, variantSellPrice, variantMRP, variant);
            productVariant.add(pVariant);
        }

        Product p = new Product(id, name, imagePath, b, null, productVariant);
        products.add(p);




    }
} catch (JSONException e) {
    e.printStackTrace();
}

代码在此行中给出了NUllpointer异常错误

for（int j = 0; j＆lt; variantArray.length（）; ++ j）{

有人可以帮我吗？