C# Generic List.Any() throws System.NullReferenceException

Question

Consider the following partial view code snippet

List<sellingPrice> Prices = ViewBag.Prices;
foreach (var mgmp in mg.messageGroup.messageGroupMessagePLUs)
{
    if (Prices.Any(x => x.pluId == mgmp.messagePLU.plu.pluId))
    {
        //do stuff
    }
}

For specific products in the db, the line

if (Prices.Any(x => x.pluId == mgmp.messagePLU.plu.pluId))

throws a System.NullReferenceException. Inspecting the code shows that mgmp is an object and Prices contains elements. However, the value of x is null. Now, I am under the impression that I am simply testing whether or not any "x" exists that satisfies my test, not asking it to return an "x".

It's a very irritating problem. Hopefully someone can point out the really obvious solution.

Dornick

Answer 1

Try:

Prices.Any(x => x!=null && x.pluId == mgmp.messagePLU.plu.pluId)

You might need to do other null checks if for example .messagePLU can be null

Overtrick

That did the trick. Thanks. I didn't think it would be necessary in my case to test for nulls in my Prices collection. Ah well, you live and learn. – Dornick

One thing to note is that this might only work wit linq-to-objects where the order is guaranteed. I'm not 100% sure but think linq-to-SQL might not short circuit correctly. – Overtrick

We'll cross that bridge when we get there. – Dornick

You can now use null propagation like (x?.pluId == mgmp.messagePLU?.plu.pluId). – Chokedamp

Answer 2

The most likely reason why this happens is because one or more items in the ViewBag.Prices is null. Check x for null, or see why prices contain nulls in the first place, assuming it's not supposed to have any null values.

Cryptonym

Answer 3

Thanks all for reasoning. An extension to check for list.Any() any even if List is null.

    /// <summary>
    /// Determines whether the collection is null or contains no elements.
    /// </summary>
    /// <typeparam name="T">The IEnumerable type.</typeparam>
    /// <param name="enumerable">The enumerable, which may be null or empty.</param>
    /// <returns>
    ///     <c>true</c> if the IEnumerable is null or empty; otherwise, <c>false</c>.
    /// </returns>
    public static bool IsNullOrEmpty<T>(this ICollection<T> enumerable)
    {
        return enumerable != null && enumerable.Count > 0;
    }

Strobel