Object reference not set error INSIDE != null only if block?

Question

Repository code:

public IQueryable<Bundle> getAllCustomBundlesByCompanyID(int companyID)
{
    return from companyBundle in db.CompanyBundles
           join bundle in db.Bundles on companyBundle.BundleID equals bundle.BundleID
           where companyBundle.CompanyID == companyID && bundle.CompanyID == companyID
           orderby bundle.BundleName ascending
           select bundle;
}

Controller code:

    ViewData["OurCategories"] = bundleRepository.getAllCustomBundlesByCompanyID(CompanyID);

View code:

    <ul class="SmallCats">
       <%if(ViewData["OurCategories"] != null){ %>
            <%List<KODmvc.Models.Bundle> ourCategories = ViewData["OurCategories"] as List<KODmvc.Models.Bundle>; %>
            <%foreach(KODmvc.Models.Bundle b in ourCategories) { %>
            <li><a href="<%=b.BundleID%>">
                <img src="/Content/images/bundleicons/<%=b.BundleIcon %>" />
                <%=b.BundleName %></a>
            </li>
            <%} %>
        <%} else { %>
            There are no custom categories.
        <%} %>

    </ul>

ERROR:

 Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 38:                <%if(ViewData["OurCategories"] != null){ %>
Line 39:                     <%List<KODmvc.Models.Bundle> ourCategories = ViewData["OurCategories"] as List<KODmvc.Models.Bundle>; %>
Line 40:                     <%foreach(KODmvc.Models.Bundle b in ourCategories) { %>
Line 41:                     <li><a href="<%=b.BundleID%>">
Line 42:                         <img src="/Content/images/bundleicons/<%=b.BundleIcon %>" />


Source File: e:\Bancroft Archive\PanamaTrunk\Views\Asset\AdminDashboard.aspx    Line: 40 

But I am checking to make sure the ViewData is not null before letting it in, what on earth??

Answer 1

Well, if the as cast doesn't match the type you supply, then it returns null. Your foreach dereferences ourCategories, which might well be null at this point.

You should use a () cast if you're not going to explicitly test ourCategories for null. Then you'll get a meaningful error if the cast fails.

Answer 2

getAllCustomBundlesByCompanyID will not return a List.

Change this line:

<%List<KODmvc.Models.Bundle> ourCategories = ViewData["OurCategories"] as List<KODmvc.Models.Bundle>; %>

To this:

<% var ourCategories = new List<KODmvc.Models.Bundle>(ViewData["OurCategories"] as IEnumerable<KODmvc.Models.Bundle>); %>

Edit

If you want to keep the lazy evaluation you can simplify the code even more.

<% foreach (var category in (IEnumerable<KODmvc.Models.Bundle>)ViewData["OurCategories"]) %>

Answer 3

Your object is an IQueryable<KODmvc.Models.Bundle>, not a List<KODmvc.Models.Bundle>.

Therefore, the expression ViewData["OurCategories"] as List<KODmvc.Models.Bundle> will equal null. If you change it to a regular cast, (List<KODmvc.Models.Bundle>)ViewData["OurCategories"], it will throw an InvalidCastException.

To solve this, you need to either change the controller method to call ToList on the IQueryable so that the model will hold a List<KODmvc.Models.Bundle>, or change the View to cast to IQueryable<KODmvc.Models.Bundle>.