Why is LINQPAD assuming this variable is a System.Int32 and how can I change its mind?

I'm trying to optimize a query so I plugged it into LINQPAD but I keep getting a null reference error, can't assign null value to System.Int32.. when I comment out the FolderID one at the end there, the error no longer occurs. Why does it assume that FolderID is a System.Int32 and how can I make it an Int32? instead so it's nullable and I can run the query?

(from groupBundle in GroupBundles
    join userGroup in UserGroups on groupBundle.GroupID equals userGroup.GroupID
    join bundle in Bundles on groupBundle.BundleID equals bundle.BundleID
    where userGroup.UserID == 75
    orderby bundle.BundleName
    select new
    {
        BundleID = bundle.BundleID,
        BundleName = bundle.BundleName,
        BundleIcon = bundle.BundleIcon,
        UseSpecialPlayer = (bundle.UseSpecialPlayer != null && bundle.UseSpecialPlayer == true) ? true : false,
        height = bundle.PuHeight,
        width = bundle.PuWidth,
        UserID = 75,
        CompanyID = 32,
  开发者_如何学编程      IsFavorite = ((from f in Favorites where f.FavoriteTypeID == 1 && f.UserID == 75 && f.ActionID == bundle.BundleID select f).Count() > 0) ? true : false,

        //THIS ONE HERE
        FolderID = (from cf in CategoryFolders 
            join folder in Folders on cf.FolderID equals folder.FolderID
            where folder.CompanyID == 32 &&
            cf.CategoryID == bundle.BundleID
            select cf.FolderID).FirstOrDefault()
}).Distinct()

Add a cast to nullable int to the expression being assigned:

FolderID = (int?)(from cf in CategoryFolders

is FolderID nullable in the database? If not, that explains this.

I'm assuming that FolderId is in a database somewhere, and I would guess that it's declared as a nullable type, perhaps even a nullable Int column.

I'm sorry I can't post this as a comment, but does just querying this work?

    //THIS ONE HERE
    FolderID = (from cf in CategoryFolders 
        join folder in Folders on cf.FolderID equals folder.FolderID
        where folder.CompanyID == 32 &&
        cf.CategoryID == bundle.BundleID
        select cf.FolderID).FirstOrDefault()