System.ArgumentNullException

The exception that is thrown when a null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

Minimum version: >= 1.1 >= Core 1.0

Statistics

How to handle it

try
{

}
catch (System.ArgumentNullException e)
{

}

try
{

}
catch (System.ArgumentNullException e) when (e.Message.Contains("something"))
{

}

try
{

}
catch (System.ArgumentNullException e) when (LogException(e))
{

}

private static bool LogException(Exception e)
{
    logger.LogError(...);
    return false;
}

How to avoid it

We haven't written anything about avoiding this exception yet. Got a good tip on how to avoid throwing System.ArgumentNullException? Feel free to reach out through the support widget in the lower right corner with your suggestions.

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Possible fixes from StackOverflow

It seams all you want to do is filter your context.Books by some criteria.

IEnumerable<Book> books = context.Books.Where(b => someConditions);

If you still need the empty IEnumerable you can just call Enumerable.Empty():

IEnumerable<Book> books = Enumerable.Empty<Book>();

I'm answering my own question.

I tried adding following in my web.config

<system.serviceModel>
  <serviceHostingEnvironment aspNetCompatibilityEnabled="true" />
</system.serviceModel>

Also decorated my Service with following attribute

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]    
public class CalculatorService : ICalculatorSession    
{
    // Implement calculator service methods
 }

Still no use. Then I got the solution here by which you can use Elmah without HTTPContext. i.e. log errors by writing

Elmah.ErrorLog.GetDefault(null).Log(new Error(ex));

instead of

Elmah.ErrorSignal.FromCurrentContext().Raise(error);

Try both Model != null and !String.IsNullOrEmpty(Model.ImageName) first, as you may be passing not only a Null value from the Model but also a Null Model:

@if (Model != null && !String.IsNullOrEmpty(Model.ImageName))
{
    <label for="Image">Change picture</label>
}
else
{ 
    <label for="Image">Add picture</label>
}

Otherwise, you can make it even neater with some ternary fun! - but that will still error if your model is Null.

<label for="Image">@(String.IsNullOrEmpty(Model.ImageName) ? "Add" : "Change") picture</label>

The NotNullAttribute is gone. It was replaced with conditionally throwing ArgumentNullException and subsequently removed by the ASP.NET team. As of Jan 12, 2016 there's no plan to bring it back. (At that time, I was working on the ASP.NET team.)

~~The attribute will be replaced through a pre-compilation step, using Roslyn, by code that does the actual check.~~

However, the feature is not yet ready as of Jun 17, 2015. It will come in a later version. So far, it is just an empty internal attribute that should be implemented in each project again:

[AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false)] internal sealed class NotNullAttribute : Attribute { }

Thanks everyone, here is my ErrorHelper class I came up with to manually log errors on websites and in WCF services, windows services, etc:

    public static class ErrorHelper
{
    /// <summary>
    /// Manually log an exception to Elmah.  This is very useful for the agents that try/catch all the errors.
    /// 
    /// In order for this to work elmah must be setup in the web.config/app.config file
    /// </summary>
    /// <param name="ex"></param>
    public static void LogErrorManually(Exception ex)
    {
        if (HttpContext.Current != null)//website is logging the error
        {                
            var elmahCon = Elmah.ErrorSignal.FromCurrentContext();
            elmahCon.Raise(ex);
        }
        else//non website, probably an agent
        {                
            var elmahCon = Elmah.ErrorLog.GetDefault(null);
            elmahCon.Log(new Elmah.Error(ex));
        }
    }
}