nullable object must have a value

Question

There is paradox in the exception description: Nullable object must have a value (?!)

This is the problem:

I have a DateTimeExtended class, that has

{
  DateTime? MyDataTime;
  int? otherdata;

}

and a constructor

DateTimeExtended(DateTimeExtended myNewDT)
{
   this.MyDateTime = myNewDT.MyDateTime.Value;
   this.otherdata = myNewDT.otherdata;
}

running this code

DateTimeExtended res = new DateTimeExtended(oldDTE);

throws an InvalidOperationException with the message:

Nullable object must have a value.

myNewDT.MyDateTime.Value - is valid and contain a regular DateTime object.

What is the meaning of this message and what am I doing wrong?

Note that oldDTE is not null. I've removed the Value from myNewDT.MyDateTime but the same exception is thrown due to a generated setter.

Strange. I reproduce the exception with the .Value there, and get no exception without the .Value there. Are you sure you're running the updated code? — Yuliy, Dec 13 '09 at 11:20
The constructor takes an instance of itself. how are you creating that first instance? — Paul Creasey, Dec 13 '09 at 11:23
it is constructed as new() without parameters, and then I add the values (it works). — Dani, Dec 13 '09 at 13:09
@Yuliy - I get the same exception if I try to set the otherdata field first. — Dani, Dec 13 '09 at 13:10
@Yuliy - I've run this code in a new project and it works as you said. I'm trying to figure out what went wrong.... — Dani, Dec 13 '09 at 13:20
Problem solved - the problem wasn't there... there was a generated setter to the otherdata and MyDateTime, that was checking the value before setting it.. flying when it's null !!! — Dani, Dec 13 '09 at 15:30
yes, the same problem i had, its only because i had null able object, — adnan, Dec 28 '16 at 12:39

score 258 · Accepted Answer · edited Dec 14 '17 at 09:59

258

You should change the line this.MyDateTime = myNewDT.MyDateTime.Value; to just this.MyDateTime = myNewDT.MyDateTime;

The exception you were receiving was thrown in the .Value property of the Nullable DateTime, as it is required to return a DateTime (since that's what the contract for .Value states), but it can't do so because there's no DateTime to return, so it throws an exception.

In general, it is a bad idea to blindly call .Value on a nullable type, unless you have some prior knowledge that that variable MUST contain a value (i.e. through a .HasValue check).

EDIT

Here's the code for DateTimeExtended that does not throw an exception:

class DateTimeExtended
{
    public DateTime? MyDateTime;
    public int? otherdata;

    public DateTimeExtended() { }

    public DateTimeExtended(DateTimeExtended other)
    {
        this.MyDateTime = other.MyDateTime;
        this.otherdata = other.otherdata;
    }
}

I tested it like this:

DateTimeExtended dt1 = new DateTimeExtended();
DateTimeExtended dt2 = new DateTimeExtended(dt1);

Adding the .Value on other.MyDateTime causes an exception. Removing it gets rid of the exception. I think you're looking in the wrong place.

edited Dec 14 '17 at 09:59

Matt

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answered Dec 13 '09 at 11:14

Yuliy

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You are right about the .value, yet something else causes the exception. I've removed the .value, and i've changed the code order of the constructor- copying the int value first, but same exception is thrown. – Dani Dec 13 '09 at 11:18
I've commented on the question - found the problem, it was in a generated setter for the properties. – Dani Dec 13 '09 at 15:31
yes, its resolved my problem, i just change null able object to non null able, and convert datetime to string directly, not by datetimeobject.value.datetime.tostring() – adnan Dec 28 '16 at 12:41
Great answer. Getting an exception calling `.Value` on a null object makes sense (I guess), but the exception message is really misleading if you happen to be dealing with two Nullable objects. Something like 'The .Value property requires the object to be non-null' would make a whole lot more sense. – DVK Aug 14 '17 at 15:11

Protector one · Answer 2 · 2020-05-15T14:28:24.137

26

When using LINQ extension methods (e.g. Select, Where), the lambda function might be converted to SQL that might not behave identically to your C# code. For instance, C#'s short-circuit evaluated && and || are converted to SQL's eager AND and OR. This can cause problems when you're checking for null in your lambda.

Example:

MyEnum? type = null;
Entities.Table.Where(a => type == null || 
    a.type == (int)type).ToArray();  // Exception: Nullable object must have a value

edited May 15 '20 at 14:28

answered Jan 21 '15 at 13:23

Protector one

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I realize this answer is not relevant to the OP's specific case, but it's relevant to the Exception he's getting. Also, this page is the first hit on Google for that exception, which makes it relevant. – Protector one Jan 21 '15 at 13:29
This was also this issue for me with null-conditional operators ("optional chaining" in Javascript) . Instead of obj?.getValue(), I needed to do obj != null && obj.getValue() – BobtheMagicMoose May 10 '22 at 13:45

score 8 · Answer 3 · edited Aug 19 '19 at 17:07

8

Try dropping the .value

DateTimeExtended(DateTimeExtended myNewDT)
{
   this.MyDateTime = myNewDT.MyDateTime;
   this.otherdata = myNewDT.otherdata;
}

edited Aug 19 '19 at 17:07

ArunPratap

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answered Dec 13 '09 at 11:12

Paul Creasey

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doesn't help. it throws the same exception if I run the 2nd line first. – Dani Dec 13 '09 at 11:14

score 2 · Answer 4 · answered Dec 13 '09 at 11:13

2

Assign the members directly without the .Value part:

DateTimeExtended(DateTimeExtended myNewDT)
{
   this.MyDateTime = myNewDT.MyDateTime;
   this.otherdata = myNewDT.otherdata;
}

answered Dec 13 '09 at 11:13

Cecil Has a Name

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score 2 · Answer 5 · answered Dec 13 '09 at 11:13

2

In this case oldDTE is null, so when you try to access oldDTE.Value the InvalidOperationException is thrown since there is no value. In your example you can simply do:

this.MyDateTime = newDT.MyDateTime;

answered Dec 13 '09 at 11:13

Lee

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The oldDTE is not null, but I removed the value anyhow... it is still throwing that exception.... – Dani Dec 13 '09 at 11:19

score 1 · Answer 6 · answered Apr 27 '23 at 05:29

1

To answer your actual question, what does "Nullable object must have a value " mean?

I think that it is a terrible error, it's saying "You are trying to take the .Value of a nullable object, but it is null".

Or they could have just said "Nullable object must have a value in order to take it's .Value"

answered Apr 27 '23 at 05:29

O'Rooney

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I agree the exception message is terribly written. The very gist of a nullable object is that it does not have to have a value! – Eike Jul 04 '23 at 14:25

score 0 · Answer 7 · answered Sep 28 '12 at 13:19

0

I got this message when trying to access values of a null valued object.

sName = myObj.Name;

this will produce error. First you should check if object not null

if(myObj != null)
  sName = myObj.Name;

This works.

answered Sep 28 '12 at 13:19

Juris

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Before answering, please try to read through the other answers for the question first - especially the accepted answer that states exactly what you placed in *your* answer. Though it doesn't show it using code, it spells it out. Also, try to make your example code relevant to the question's - such as `this.MyDateTime = myNewDT.MyDateTime.Value;`, not `sName = myObj.Name;` – newfurniturey Sep 28 '12 at 17:58

score 0 · Answer 8 · answered Dec 13 '09 at 11:14

0

Looks like oldDTE.MyDateTime was null, so constructor tried to take it's Value - which threw.

answered Dec 13 '09 at 11:14

Pavel Radzivilovsky

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score 0 · Answer 9 · answered Jul 08 '20 at 07:10

0

I got this solution and it is working for me

if (myNewDT.MyDateTime == null)
{
   myNewDT.MyDateTime = DateTime.Now();
}

answered Jul 08 '20 at 07:10

KKG

1

MSH · Answer 10 · 2023-08-31T02:03:15.293

0

Use

`DateTimeExtended(DateTimeExtended myNewDT)
{
   this.MyDateTime = myNewDT.MyDateTime.**GetValueOrDefault();**
   this.otherdata = myNewDT.otherdata;
}`

It'll simply check the value and set Null if there is no value.

> .Value

Must only be used when you are sure it's coming. But as you are not sure, you simply use ".GetValueOrDefault()"

edited Aug 31 '23 at 02:03

answered Aug 31 '23 at 01:57

MSH

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Thank you for your interest in contributing to the Stack Overflow community. This question already has quite a few answers—including one that has been extensively validated by the community. Are you certain your approach hasn’t been given previously? **If so, it would be useful to explain how your approach is different, under what circumstances your approach might be preferred, and/or why you think the previous answers aren’t sufficient.** Can you kindly [edit] your answer to offer an explanation? – Jeremy Caney Sep 01 '23 at 00:29

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