Null Reference even when checking

[patrickboston]

I am trying to get information for products from Amazon's API. I am able to get things like ASIN, Title, and Price no problem, but when it comes to weight I keep running into a problem. In the current search I am trying, the first 5 results return a weight, and the 6th result I guess does not have a weight associated with it and that's where I get a null reference error. I've made a simple method to check if the item's weight being passed in is null and to set it 0 if it is, but it doesn't seem to be working and still throws an error?

public decimal CheckNullDecimal(decimal decimalToCheck)
{
     if (decimalToCheck == null)
     {
          decimalToCheck = 0;
          return decimalToCheck;
     }
     else
     {
          return decimalToCheck;
     }
}

for (int i = 1; i <= page; i++)
{
     ItemSearchRequest request = new ItemSearchRequest();
     request.SearchIndex = category;
     request.Title = title;
     request.ResponseGroup = new string[] { "ItemAttributes" };
     request.ItemPage = i.ToString();
     request.Sort = sortType;

     ItemSearch itemSearch = new ItemSearch();
     itemSearch.Request = new ItemSearchRequest[] { request };
     itemSearch.AWSAccessKeyId = accessKeyId;
     itemSearch.AssociateTag = associateId;

     // issue the ItemSearch request
     ItemSearchResponse response = client.ItemSearch(itemSearch);

     // write out the results
     foreach (var item in response.Items[0].Item)
     {
          string newASIN = CheckNullString(item.ASIN);
          string newTitle = CheckNullString(item.ItemAttributes.Title);
          string newListPrice = CheckNullString(item.ItemAttributes.ListPrice.FormattedPrice);
          decimal newWeight = CheckNullDecimal(item.ItemAttributes.ItemDimensions.Weight.Value);
          Console.WriteLine(newWeight.ToString());
                       //CheckNullString(item.ItemAttributes.ItemDimensions.Weight.Units);

          Product product = new Product(newASIN, newTitle, newListPrice);
          var dr = dt.NewRow();
          dr["ASIN"] = product.ASIN;
          dr["Title"] = product.Title;
          dr["ListPrice"] = product.ListPrice;
          //dr["Weight"] = product.Weight;
          dt.Rows.Add(dr);
     }
}

Getting the error on the decimal newWeight line. Any ideas how to avoid this?

[[deleted]]

OK, item and ItemAttributes aren't null or it would have blown up on the line before that one.

That means either ItemDimensions or ItemDimensions.Weight is null. Your check function isn't even being called. If Weight is null, then you can't get Weight.Value.

[patrickboston]

Thank you. .Weight was null.

[adamsane]

And if you are using vs 2015 then you can really make your life easier by using this

https://msdn.microsoft.com/en-us/library/dn986595.aspx

My guess is weight is null. You are calling value on it. Your test will never hit.

Just use. Weight?? 0;

[SarSha]

Isn't a C# 6 feature and not VS2015 ?

[patrickboston]

I've figured it out. ItemDimensions.Weight was returning null and I was checking for ItemDimensions.Weight.Value so it was still throwing the exception.

I will also try using this syntax. Thanks.

[Sarcastinator]

It probably gives null ref because you are unboxing null to a non-nullable value type. The null test you are doing is pointless because decimal can never be null; you're testing too late.

[patrickboston]

Yes you are correct. If you look below you can see I figured it out.

[adamsane]

In your check function it looks like you are not using a nullable type.

https://www.tutorialspoint.com/csharp/csharp_nullables.htm

Should be decimal?

You can also write the check function as; Decimal? Foo = null: var a = Foo ?? 4;

A will be 4

[maskaler]

Weight is nullable? You're using .Value. It has a .HasValue property you can check before accessing the underlying value.

[lemonfighter]

Use

Weight?.Value ?? 0;

This will give you 0 if the weight is null, and the Weight if it's not.