LINQ left outer join NullReferenceException - linq

Question

I am getting NullReferenceException when doing left outer join.
Similar query works in LINQ Pad but not in Visual Studio 2015. System.NullReferenceException was unhandled by user code
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Thanks in advance.
.Net Core LINQ Code that does not work:
public IEnumerable<R> GetAll()
{
var results =
from a in uow.R.GetAll()
join b in uow.SSR.GetAll() on a.ID equals b.RID into g9
from c in g9.DefaultIfEmpty()
join d in uow.SS.GetAll() on c.SSID equals d.ID into g10
from e in g10.DefaultIfEmpty()
select new
{
a.Id,
SSID = c == null ? null : (int?)c.SSID,
e.Name
};
List<R> rList = new List<R>();
foreach (var a in results)
{
resourceList.Add(new R { ID = a.Id, SSID = a.SSID });
}
return rList.ToArray<R>();
}
`
var Result =
from a in Tbl_R
join b in Tbl_SS on a.ID equals b.RID into g9
from c in g9.DefaultIfEmpty()
join d in Lu_SS on c.SSID equals d.SSID into g10
from e in g10.DefaultIfEmpty()
select new
{
a.ID,
SSID = c == null ? null : (int?)c.SSID,
e.Name
};
Result.Dump();
SELECT t2.ID,
ISNULL(t17.SSID,'') as SSID
ISNULL(t17.Name,'') as Name
FROM R t2
LEFT JOIN SSR t16 ON t16.RID=t2.ID
LEFT JOIN SS t17 ON t16.SSID=t17.SSID