Properly handling possible System.NullReferenceException in lambda expressions

Question

Here's the query in question

return _projectDetail.ExpenditureDetails
    .Where(detail => detail.ProgramFund == _programFund
         && detail.Expenditure.User == _creditCardHolder)
    .Sum(detail => detail.ExpenditureAmounts.FirstOrDefault(
        amount => amount.isCurrent && !amount.requiresAudit)
    .CommittedMonthlyRecord.ProjectedEac);

Table Structure
ProjectDetails (1 to Many) ExpenditureDetails
ExpenditureDetails (1 to Many) ExpenditureAmounts
ExpenditureAmounts (1 to 1) CommittedMonthlyRecords

ProjectedEac is a decimal field on the CommittedMonthlyRecords.

The problem I discovered in a Unit test (albeit an unlikely event), that the following line could be null:

detail.ExpenditureAmounts.FirstOrDefault(
    amount => amount.isCurrent && !amount.requiresAudit)

My original query was a nested loop, in where I would be making multiple trips to the database, something I don't want to repeat. I've looked in to what seemed like some similar questions here, but the solution didn't seem to fit.

Any ideas?

Answer 1

Why not just check for the null?

return _projectDetail.ExpenditureDetails.Where(detail => 
        detail.ProgramFund == _programFund && 
        detail.Expenditure.User == _creditCardHolder
    ).Sum(detail => {
        var a = detail.ExpenditureAmounts.FirstOrDefault(
            amount => amount.isCurrent && !amount.requiresAudit
        );
        return a != null ? a.CommittedMonthlyRecord.ProjectedEac : 0.0m;
    });