decimal? with Left outer join gets null reference in LINQ - linq

Question

I am trying to do left outer join in LINQ for two vars but on selecting required coloumns, I get Object reference not set to an instance of an object error where I want Nullable decimal.
var FLS = (from ee in SumTillFYEnd
join es in SumTillFYStart on ee.Account equals es.Account into temp
from t in temp.DefaultIfEmpty()
select new
{
Account = ee.Account, // As of here it works
BeginDr = (t.DrStartCF == 0) ? (decimal?) null : t.DrStartCF // Here I get error Object reference not set to an instance of an object.
});
Some times SumTillFYEnd and some times SumTillFYStart becomes null. I want to join should work with default values, in case any one or both is null.

Answer 1

The problem is attempting to cast null to decimal?. You cannot ever directly cast null to another type, nullable or not. That will always cause a NullReferenceException. What you want instead is default. In other words, replace:
(decimal?)null
With
default(decimal?)

Answer 2

I solved this using a default class.
The reason I am seeing is that decimal can not be null so it either needs to set for a default value either 0 or decimal.MinValue
So, you require to have default class for SumTillFYStart like
var defaultSumTillFYStart = new SumTillFYStart { Account = string.Empty, DrStartCF =0};
With above in context, then in your piece of code replace
from t in temp.DefaultIfEmpty()
with this
from t in temp.DefaultIfEmpty(defaultSumTillFYStart)
I have a linqPad working written below but for different subset; I think it will help somebody:
void Main()
{
List<Debtor> debtors = new List<Debtor>();
List<SecurityHolding> holdings = new List<SecurityHolding>();
//Initialize Debtor
debtors.Add(new Debtor(){
AccountId = "J1",
OutstandingValue = 501.95M
});
debtors.Add(new Debtor(){
AccountId = "J2",
OutstandingValue = 75.68M
});
debtors.Add(new Debtor(){
AccountId = "J3",
OutstandingValue = 100.01M
});
//Initialize Security Holding
holdings.Add(new SecurityHolding(){
AccountId = "J2",
SecurityHoldingValue = 100M
});
holdings.Add(new SecurityHolding(){
AccountId = "J3",
SecurityHoldingValue = 200M
});
var defaultHolding = new SecurityHolding { AccountId= string.Empty, SecurityHoldingValue = 0};
var result = (from d in debtors
join p in holdings
on d.AccountId equals p.AccountId into temp
from t in temp.DefaultIfEmpty(defaultHolding)
select new
{
AccountId = d.AccountId,
OutstandingValue = d.OutstandingValue,
HoldingValue = (decimal?)t.SecurityHoldingValue
});
result.Dump();
}
// Define other methods and classes here
public class Debtor
{
public string AccountId {get;set;}
public decimal OutstandingValue {get;set;}
}
public class SecurityHolding
{
public string AccountId {get;set;}
public decimal SecurityHoldingValue {get;set;}
}
Here the output: