SPListItem item["Author"] throws ArgumentException on blog lists only for some users

Question

We have a webpart on our SiteCollection home page which aggregates the most recent posts from a number of blog subsites. The code looks like this:

using (SPSite site = new SPSite(GetBlogSiteCollectionUrl()))
        {
            foreach (SPWeb currentWeb in site.OpenWeb().GetSubwebsForCurrentUser())
            {
                if (!currentWeb.IsRootWeb)
                {
                    try
                    {
                        (from p in currentWeb.Lists["Posts"].Items.OfType<SPListItem>()
                         where (string)p["Approval Status"] == "0"

                         select new BlogPost
                         {
                             Title = p["Title"] == null ? string.Empty : p["Title"].ToString(),
                             Url = p["FileDirRef"].ToString() + "/Post.aspx?ID=" + p["ID"].ToString(),
                             Author = BlogPostHelper.GenerateAuthor(p["Author"].ToString()),
                             Date = Convert.ToDateTime(p["PublishedDate"].ToString()),
                             FullText = p["Body"] == null ? string.Empty : p["Body"].ToString(),
                             NewsFeed = new NewsDataFetcherImplementation() { ID = currentWeb.ID, Name = currentWeb.Title, Url = p["FileDirRef"].ToString() + "/Post.aspx?ID=" + p["ID"].ToString() },
                             Snippet = BlogPostHelper.GenerateSnippet(p["Body"] == null ? string.Empty : p["Body"].ToString(), _snippetLength),
                         }).ToList().ForEach(post => allPosts.Add(post));
                    }
                    catch (Exception ex)
                    {
                        Logger.LogException(ex, LogCategory.BlogFetcher,"Error fetching posts from {0}".FormatIt(currentWeb.Name));
                    }
                }
            }
        }
        return allPosts.OrderByDescending(m => m.Date).Take(numItems).ToList();

BlogPost is a entity class custom to our project.

The problem we are getting is that for some users, the call to p["Author"] throws this error:

System.ArgumentException: Value does not fall within the expected range

But only on one of the blog sub sites, and only for a few users. (haven't tried enough users to establish a pattern, other than it only occurs for non-admin users)

While debugging the issue, I put in the following watches:

p   {Microsoft.SharePoint.SPListItem}   Microsoft.SharePoint.SPListItem
p["ID"] 11  object {int}
p["PublishedDate"]  {2/10/2012 6:53:00 PM}  object {System.DateTime}
p["Approval Status"]    "0" object {string}
p["Author"] 'p["Author"]' threw an exception of type 'System.ArgumentException' object {System.ArgumentException}
p["Created By"] 'p["Created By"]' threw an exception of type 'System.ArgumentException' object {System.ArgumentException}
p[SPBuiltInFieldId.Author]  'p[SPBuiltInFieldId.Author]' threw an exception of type 'System.ArgumentException'  object {System.ArgumentException}
p.Properties["Author"]  null    object
p.Properties["Created By"]  null    object

Answer 1

You're calling a method on a null value:

p["Author"].ToString() <-- Error is here
p.Properties["Author"] <-- null

You should perform a check against this value to make sure it's not null.

Aside from that though, I couldn't tell you why there is no author associated with that post without more information, but that's something to look into. Do you know who the author of post ID=11 is?