Linq Join table AND nullable variable - linq

Question

I'm trying to make a LINQ Query on Ef6 using a join on the db.ClincalAssets table where the AssetDisposalID Field is null
i.e. I don't want rows of data from that table where the AssetDisposalID is not null
The following code doesn't appear to work because it returns the same 23 results I had before I modified the code
var today = DateTime.Now.Date;
var tomorrow = today.AddDays(30);
var dateresult = db.ClinicalINSs.GroupBy(d => d.ClinicalAssetID)
.SelectMany(g => g.OrderByDescending(d => d.NextInspectionDate)
.Take(1));
var ClinicalIDVM = (from s in dateresult.Where(q => q.NextInspectionDate <= tomorrow)
join co in db.ClinicalAssets.Where (t => t.AssetDisposalID == null) on s.ClinicalAssetID equals co.ClinicalAssetID into AR
let subred = AR.OrderByDescending(subredASS => subredASS.ClinicalAssetID).FirstOrDefault()
join cp in db.ClinicalPATs on s.ClinicalAssetID equals cp.ClinicalAssetID into AP
let subpat = AP.OrderByDescending(SubPATASS => SubPATASS.ClinicalAssetID).FirstOrDefault()
orderby s.NextInspectionDate descending
select new ClinicalIDVM
{
ClinicalAssetID = s.ClinicalAssetID,
ProductName = subred.ProductName ,
SerialNo = subred.SerialNo == null ? "" : subred.SerialNo,
InspectionDate = subpat.InspectionDate,
NextInspectionDate = s.NextInspectionDate == null ? (DateTime?)null : s.NextInspectionDate,
}).ToList();
i have also tried this:
var today = DateTime.Now.Date;
var tomorrow = today.AddDays(30);
var dateresult = db.ClinicalINSs.GroupBy(d => d.ClinicalAssetID)
.SelectMany(g => g.OrderByDescending(d => d.NextInspectionDate)
.Take(1));
var ClinicalIDVM = (from s in dateresult from Disp in db.ClinicalAssets where s.NextInspectionDate <= tomorrow && Disp.AssetDisposalID == null
join co in db.ClinicalAssets on s.ClinicalAssetID equals co.ClinicalAssetID into AR
let subred = AR.OrderByDescending(subredASS => subredASS.ClinicalAssetID).FirstOrDefault()
join cp in db.ClinicalPATs on s.ClinicalAssetID equals cp.ClinicalAssetID into AP
let subpat = AP.OrderByDescending(SubPATASS => SubPATASS.ClinicalAssetID).FirstOrDefault()
orderby s.NextInspectionDate descending
select new ClinicalIDVM
{
ClinicalAssetID = s.ClinicalAssetID,
ProductName = subred.ProductName ,
SerialNo = subred.SerialNo == null ? "" : subred.SerialNo,
InspectionDate = subpat.InspectionDate,
NextInspectionDate = s.NextInspectionDate == null ? (DateTime?)null : s.NextInspectionDate,
}).ToList();
but I get al records duplicated.