How to check for NullReferenceException in LINQ result - wpf

Question

I have a LINQ query that works fine with EF in my DAL:
using (var mLEntities = new myLab02Entities1())
{
var test = from c in mLEntities.Chemicals
from u in c.Usages
select new
{
cChemID = c.Chem_ID,
c.Name,
c.Supplier,
c.Grade,
c.OrderNo,
c.BatchNo,
c.EntryDate,
c.CreatedBy,
cUser = u.Person.PersName,
uChemID = u.Chem_ID,
u.Study_ID,
u.UsedBy,
uUser = u.Person.PersName,
u.UseDate,
u.Project.StudyNo,
u.Project.ProjectName,
};
Usages is a Navigation property of Chemicals (1 chem : n usa), and Person and Projects are both Navigation properties of Usages (both 1 : 1).
Then I wanted to put this query in my Business Logic and wrote:
IList<ChemicalBDO> chemicalListBDO = chemListDAO.GetChemicalsListFromDB();
var test = from c in chemicalListBDO
from u in c.Usages
select new
{
cChemID = c.Chem_ID,
c.Name,
c.Supplier,
c.Grade,
c.OrderNo,
c.BatchNo,
c.EntryDate,
c.CreatedBy,
cUser = u.Person.PersName,
uChemID = u.Chem_ID,
u.Study_ID,
u.UsedBy,
uUser = u.Person.PersName,
u.UseDate,
u.Project.StudyNo,
u.Project.ProjectName
};
That is, I first query my EF DBcontext and get my Chemicals Entity, and than I write a query against this Chemicals Entity.
For me the strange thing is that the last Code throws a System.NullReferenceExeption, because u.Person and u.Project can be NULL. But the first query does not throw exceptions, what is the reason for that?
How can I handle the NULL reference in the select query, can I check for NULL with "if", "?" or "??" ?
Btw: I thought having the complex query in the DAL is no good programming practice, is that true or can I let the Code there?
Any help is appreciated.

Answer 1

This should fix this problem:
IList<ChemicalBDO> chemicalListBDO = chemListDAO.GetChemicalsListFromDB();
var test = from c in chemicalListBDO
from u in c.Usages
select new
{
cChemID = c.Chem_ID,
c.Name,
c.Supplier,
c.Grade,
c.OrderNo,
c.BatchNo,
c.EntryDate,
c.CreatedBy,
cUser = u.Person != null ? u.Person.PersName : string.Empty,
uChemID = u.Chem_ID,
u.Study_ID,
u.UsedBy,
uUser = u.Person != null ? u.Person.PersName : string.Empty,
u.UseDate,
u.Project != null ? u.Project.StudyNo : -1,
u.Project != null ? u.Project.ProjectName : string.Empty
};