No result in LINQ query gives Object reference not set to an instance of an object in IF ELSE statement

Question

I have the following code:

        DataClasses1DataContext db = new DataClasses1DataContext();

        var UserInfo = db.Users.FirstOrDefault(u => u.Email == TextBox1.Text);

        if (UserInfo.Email != null)
        {
            Label2.Text = "Email is not null";
        }
        else
        {
            Label2.Text = "Email is null";
        }

If an e-mail address exists in the table, it successfully prints "Email is not null." However, if there is no matching record, I then receive an Object reference not set to an instance of an object error for Line 29:

Line 27:             DataClasses1DataContext db = new DataClasses1DataContext();
Line 28: 
Line 29:             var UserInfo = db.Users.FirstOrDefault(u => u.Email == TextBox1.Text);
Line 30: 
Line 31:             if (UserInfo.Email != null)

I'm stumped! Any help would be greatly appreciated.

Solution 1

You might want to check for null in the predicate, but if it's a real database it shouldn't be necessary:

var UserInfo = db.Users.FirstOrDefault(u => u != null &&
                                            u.Email == TextBox1.Text);

But more importantly, there's an obvious error in your code on line 31. If FirstOrDefault doesn't find a matching object, it doesn't return an object with all fields set to null. It returns a null reference - i.e. no object at all. You need to test for that:

if (UserInfo != null)
{
    Label2.Text = "User found";
}
else
{
    Label2.Text = "User not found";
}

In my opinion you should fix the obvious error first, then update your question with the correct code if you are still having problems.

Solution 2

var UserInfo = db.Users.FirstOrDefault(u => u.Email == TextBox1.Text);

You can only get a null ref exception on this line if db or TextBox1 or TextBox1.Text is null. All are doubtful. I think you have the wrong line.

Comments

[Geir-Tore Lindsve]

The exception should come on line 31 in that case

[Mark Byers]

What about if db.Users or u is null? Also Textbox1.Text being null shouldn't give an exception. The equality test should just return false.

[Amy B]

u never acquires a value (null or otherwise): it's just a lambda expression parameter that is used to generate an expression tree to generate some sql. db.Users is very unlikely to be null, but I suppose possible. You are right about Textbox1.Text

[Carl G]

I believe u could acquire null in LINQ-to-Objects. The question mentions a "table", suggesting LINQ-to-SQL, but worth mentioning since this distinction can be tricky.

[Amy B]

The code in the question says "DataContext". The question is also tagged linq-to-sql. Putting LinqToObjects information in here would be confusing.