NullReferenceException when using Null-conditional Operator with object initializer

Question

Why I get System.NullReferenceException running a code like:

var Response = new Response()
{
    Id = request?.Event.Id
};

Shouldn't I just get Null value for Id property (Id is a string)?

@mjwills well that works, but why I have to use question mark everywhere? Shouldn't it stop executing the statement on first null? — Lesmian, Dec 10 '17 at 10:55
Your current code only take into account if `request` is `null` and `Event` will not be returned if that was the case. If `Event` is `null` in the `request` instance then that would still lead to an NRE when you try to access the `Id` property. — Igor, Dec 10 '17 at 10:56
@Igor Ok, I'll walk myself out... Apparently, I stay at work to long. I see my obvious mistake now :) — Lesmian, Dec 10 '17 at 10:59
https://stackoverflow.com/questions/2080647/deep-null-checking-is-there-a-better-way would likely be a 'better' duplicate than the one that was chosen. — mjwills, Dec 10 '17 at 11:02

score 2 · Accepted Answer · answered Dec 10 '17 at 11:00

Your current code only take into account if request is null and Event will not be returned if that was the case. If Event is null in the request instance then that would still lead to an NRE when you try to access the Id property.

The fix is to also add the null conditional operator to Event which will return null if Event is null and not try to access Id.

request?.Event?.Id

NullReferenceException when using Null-conditional Operator with object initializer

1 Answers1