C# Saving in loop error

I get an error "Object reference not set to an instance of an object." when trying to save all items from a listbox with this method.

  writer = new StreamWriter(saveBox.File开发者_Go百科Name);
   foreach (var item in LstResults.Items.Cast<object>().Where(item =>  string.IsNullOrEmpty(item.ToString())))
                    {
                        writer.Write(item.ToString().Trim() + ",");
                    }
                    writer.Close();

What am I doing wrong? The list is holding about 80k items.

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Shouldn't this be

item =>  !string.IsNullOrEmpty(item.ToString())

for this loop to make sense? If you are pulling back items which have a null ToString() result, you're then calling Trim on a null object.

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The following are your suspects:

• saveBox
• item (one of the items in the ListBox)
• the result of item.ToString (very unlikely)

If any of the ListBox's items is null, you're getting an exception on that first ToString call.