I am trying to display a nullable date time in my JSON response. In my MVC Controller I am running the following query:

var requests = 
    (from r in _context.TestRequests
     where r.scheduled_time == null && r.TestRequestRuns.Count > 0
     select new
     {
       id = r.id,
       name = r.name,
       start = DateAndTimeDisplayString(r.TestRequestRuns.First().start_dt),
       end = r.TestRequestRuns.First().end_dt.HasValue 
                ? DateAndTimeDisplayString(r.TestRequestRuns.First().end_dt.Value)
                : string.Empty
      });

When I run requests.ToArray() I get the following exception:

Could not translate expression '
 Table(TestRequest)
   .Where(r => 
    ((r.scheduled_time == null) AndAlso (r.TestRequestRuns.Count > 0)))
   .Select(r => new <>f__AnonymousType18`4(id = r.id, name = r.name, 
          start = value(QAWebTools.Controllers.TestRequestsController).
              DateAndTimeDisplayString(r.TestRequestRuns.First().start_dt), 
          end = IIF(r.TestRequestRuns.First().end_dt.HasValue,
                 value(QAWebTools.Controllers.TestRequestsController).
           DateAndTimeDisplayString(r.TestRequestRuns.First().end_dt.Value),
               Invoke(value(System.Func`1[System.String])))))' 
into SQL and could not treat it as a local expression.

If I comment out the end = line, everything seems to run correctly, so it doesn't seem to be the use of my local DateAndTimeDisplayString method, so the only thing I can think of is Linq to Sql doesn't like Ternary operators? I think I've used ternary operators before, but I can't remember if I did it in this code base or another code base (that uses EF4 instead of L2S).

Is this true, or am I missing some other issue?