title: How to add item to IEnumerable SelectListItem
body: <p>I am trying to add an item to an IEnumerable SelectList. I have an initial query that populates my list, I then have a query to check to see if an item called "INFORMATIONAL" exists. If not, I need to add it to the list returned from my initial query. Here is my code. It does not like list.Add(newItem). Any assistance would be appreciated. Thanks</p>
  
  <pre><code>public IEnumerable&lt;SelectListItem&gt; GetCategoriesByAccountID(string AccountID)
      {
          IEnumerable&lt;SelectListItem&gt; list = null;
  
          using (var context = new AMPEntities())
          {
              // Queries DB for list of categories by AccountID
              var query = (from ca in context.CustomAlerts
                          where ca.AccountID == AccountID
                          orderby ca.AlertCategory
                          select new SelectListItem { Text = ca.AlertCategory, Value = ca.AlertCategory }).Distinct();
              list = query.ToList();
  
              // Checks list to see if "INFORMATIONAL" already exists
              var item = (from l in list
                          where l.Value == "INFORMATIONAL"
                          select new SelectListItem { Text = l.Text, Value = l.Value }).FirstOrDefault();
  
              // If "INFORMATIONAL" is not present add it to list
              if (item == null)
              {
                  var newItem = new SelectListItem { Text = "INFORMATIONAL", Value = "INFORMATIONAL" };
                  list.Add(newItem);
              }
          }
  
          return list;
      }
  </code></pre>