FluentValidation NullReferenceException - Way to prevent checking for null values?

Question

If I have something like this:

When(x => x.SendMail.Equals("Y"), () =>
{
    RuleFor(x => x.To).NotEmpty();
    RuleFor(x => x.From).NotEmpty();
    RuleFor(x => x.EmailAddress).NotEmpty();
});

and SendMail does not have a value, I will get a NullReferenceException. However, if I surround the When() like so:

When(x => x.SendMail != null, () =>
{
    When(x => x.SendMail.Equals("Y"), () =>
    {
        RuleFor(x => x.To).NotEmpty();
        RuleFor(x => x.From).NotEmpty();
        RuleFor(x => x.EmailAddress).NotEmpty();
    });
});

it works as I would expect and I do not get a NRE when SendMail does not have a value. I'm new to FluentValidaton and C# in general. Is this the proper way to go about handling validations like this? Do I need to wrap all logic like this with null checks?

Are you able to do When(x => x.SendMail != null && x.SendMail.Equals("Y"),...); — Nkosi
– Nkosi, Commented Feb 1, 2017 at 20:23

Igor · Accepted Answer · 2017-02-01 20:46:32Z

4

The easiest thing to do is just switch the comparison.

When(x => x.SendMail.Equals("Y"), () => // etc

becomes

When(x => "Y".Equals(x.SendMail), () => // etc

This works because "Y" is never null (so the Equals method can be called which is where your current code fails) and will also not throw an NRE when doing a comparison inside of the Equals method as a null value will simply return false.

answered Feb 1, 2017 at 20:46

Igor

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3 Comments

Nkosi Over a year ago

I like this answer. I am wondering now if object.Equals("Y", x.SendMail) is also a good option?

Igor Over a year ago

@Nkosi - I don't see why not or string.Equals as well if the OP wanted to do a case insensitive comparison by including a StringComparison parameter.

Nkosi Over a year ago

That makes sense. wasn't sure if "Y" was a mcve stand in.

Alexander V. · Accepted Answer · 2017-02-01 20:24:10Z

3

I would recommend to do something like this

When(x => x.SendMail != null && x.SendMail.Equals("Y"), () =>
{
    RuleFor(x => x.To).NotEmpty();
    RuleFor(x => x.From).NotEmpty();
    RuleFor(x => x.EmailAddress).NotEmpty();
});

This way second condition of and statement (x.SendMail.Equals("Y")) evaluates only if first one (x.SendMail != null) is true. This rule it works for any boolean expression.

answered Feb 1, 2017 at 20:24

Alexander V.

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Comments

Nkosi · Accepted Answer · 2017-02-01 20:38:55Z

2

What you are doing can be simplified to

When(x => x.SendMail != null && x.SendMail.Equals("Y"), () =>
{
    RuleFor(x => x.To).NotEmpty();
    RuleFor(x => x.From).NotEmpty();
    RuleFor(x => x.EmailAddress).NotEmpty();
});

Or if using latest version c#

When(x => x.SendMail?.Equals("Y") ?? false, () =>
{
    RuleFor(x => x.To).NotEmpty();
    RuleFor(x => x.From).NotEmpty();
    RuleFor(x => x.EmailAddress).NotEmpty();
});

edited Feb 1, 2017 at 20:38

answered Feb 1, 2017 at 20:27

Nkosi

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Comments

dawid · Accepted Answer · 2017-02-01 20:42:27Z

0

@Ryan Buening you are trying to call instance method of null object so you are getting NullReferenceException and this is normal for c#. I think you could use null conditional operator from c#6

When(x => x.SendMail?.Equals("Y"), () =>
{
    RuleFor(x => x.To).NotEmpty();
    RuleFor(x => x.From).NotEmpty();
    RuleFor(x => x.EmailAddress).NotEmpty();
});

answered Feb 1, 2017 at 20:42

dawid

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1 Comment

Tseng Over a year ago

There is no need to repeat what others have posted long before your answer

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