>I have this:
>
>

>
>var query = from g in root.Groups
>            from r in g.Rules
>            from c in r.Conditions
>            from a in c.Actions
>            where g.Rules != null
>            where r.Conditions != null
>            where c.Actions != null
>            where a.ActionID == ActionId
>            select a;
>
>List<RuleAction> items = query.ToList();
>RetVal = items[0];

>
>
>It fails on the last line with "Object reference not set to an instance of an object" because the query returned no results.
>
>How do I test for this before attempting to convert the results to a list?

Test the items for zero length? Maybe:

RetVal = items.Count==0 ? null : items[0];