This report works fine when I'm just reporting Assets with Owners but I want to report on Assets without owners so added the Null criteria but it didn't work. How can I get it to report on assets without owners?
Select Top 1000000 tblAssets.AssetID,
  tblAssets.AssetUnique,
  tblAssets.Description,
  tblBaseBoard.Manufacturer,
  tblBaseBoard.Product As Motherboard,
  tblProcessor.Name As Processor,
  Ceiling(tblAssets.Memory / 1024) As Ram,
  tblAssetUserRelations.Username,
  tblAssets.Firstseen,
  tblAssetCustom.PurchaseDate,
  tblState.Statename,
  tblOperatingsystem.Caption
From tblComputersystem
  Inner Join tblAssets On tblComputersystem.AssetID = tblAssets.AssetID
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tblBaseBoard On tblAssets.AssetID = tblBaseBoard.AssetID
  Inner Join tblProcessor On tblAssets.AssetID = tblProcessor.AssetID
  Inner Join tblAssetUserRelations On tblAssets.AssetID =
    tblAssetUserRelations.AssetID
  Inner Join tblState On tblState.State = tblAssetCustom.State
  Inner Join tblOperatingsystem
    On tblAssets.AssetID = tblOperatingsystem.AssetID
Where (tblAssetUserRelations.Username Is Null) Or
  (tblAssetUserRelations.Username = N'')
Order By tblAssets.AssetName