Error details: Value cannot be null. Parameter name: key

Question

When I try to export data into excel in editable grid screen I get this error

An error occurred while running the screen. You can close the screen or ignore the error and continue using the screen. Error details: Value cannot be null. Parameter name: key

What does it mean ? 

Answer 1

That would be a NullReferenceException.

Run your project in debug up to the point when you are about to get this error then go to the VS IDE and click Debug | Exceptions, tick the box next to Common Language Runtime Exceptions and click OK. Now click the Export to Excel button in your application and, with a little luck, you should drop into the code editor at the point the error occurs. If you hover the mousepointer on all the variables in the line that has errored you might be able to fine out which one is Null (Nothing in VB).

Don't forget to go back to the Exceptions dialog and click Reset All to turn exception handing back to normal.

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Simon Jones
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Answer 2

That would be a NullReferenceException.

It's actually an ArgumentNullException.

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Justin Anderson, LightSwitch Development Team

Answer 3

Pardon me for not being quite awake.

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Simon Jones
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Answer 4

Thanks for the tip but, as you mentioned it didn't drop into code editor. You think this could be the culprit ?

 partial void q59_HowSTI_other_Validate(EntityValidationResultsBuilder results)
        {
            if (this.q59_HowSTI_other != null && !System.Text.RegularExpressions.Regex.IsMatch(this.q59_HowSTI_other, @"^[a-zA-Z]+$"))
            {
                results.AddPropertyError("Only alphabets allowed.");
            }

        }

I commented the above code and tried again still same problem.

Answer 5

No, I don't think it can be that code that is causing the exception.

1) You have coded to cope with this.q59_HowSTI_other being null

2) You have tried commenting out the code and the error still occurs.

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Simon Jones
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Answer 6

How to identify the problem then ? I found these could be the problems too 

1)

. LS table with a many to zero or 1 relationship with a view off a database where the summary field for the view is a required field (such as name or ID) throws an error if left empty.

Exception: Value cannot be null. Parameter name: body

2)

The key here is "Value cannot be null". Parameter name is misleading. This is telling you that an entity was retrieved and it has a required field containing a null value

Error launching the screen. Error : Value cannot be null. Parameter name: screen

I used to have table with many to  zero or one but I did update my data model. I'm using vs2011 beta.

Answer 7

We do not have enough information in order to diagnose the problem which is why I suggested turning on all exception trapping. That usually leads you to the problem.

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Simon Jones
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Answer 8

I've got the same problem when upgrading to LS2Beta. It seems that when using a 'Data Item' which is empty it creates this problem.

To reproduce add a Data Item of type Query return type Single or Default of a random table. Run the application and open screen. (or try the link in my thread below).

See my thread

How Do I: Create a Screen that can Both Edit and Add Records in a LightSwitch Application?" in LightSwitch 2 Beta

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rdk

Answer 9

I encountered the same issue as Jason describes in the first message above.

I found the following information in the debug messages:

{System.ArgumentNullException: Value cannot be null.

Parameter name: key
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.LightSwitch.Details.Framework.Internal.StringValueConversion.SupportedValueStringValueStringValueConverter.Microsoft.LightSwitch.Details.Framework.Internal.StringValueConversion.IStringValueConverter.ConvertToString(Object value, CultureInfo culture)
   at Microsoft.LightSwitch.Details.Framework.Internal.StringValueConversion.DefaultDataFormatter.Microsoft.LightSwitch.Runtime.DataFormatter.IDataFormatter.FormatData(Object value)
   at Microsoft.LightSwitch.Runtime.Services.Implementation.EntityExportService.DataTable.FormatColumn(Int32 index, IDataOutputPort device)
   at Microsoft.LightSwitch.Runtime.Services.Implementation.ExcelDataOutputPort.ExcelDataOutputSession.FormatData(IDataTable dataTable)
   at Microsoft.LightSwitch.Runtime.Services.Implementation.ExcelDataOutputPort.ExcelDataOutputSession.SendData(Object data)
   at Microsoft.LightSwitch.Presentation.Implementation.Controls.ExportCollectionDataCommand.<>c__DisplayClass8.<Execute>b__2()}

Any ideas?

Thanks for your help!

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Thanks, Edgar Walther

Answer 10

I had a the same problem with exporting a VisualCollection which had a field with a choice list.

If the field is not required, it might be empty. Trying to find the choice for the key gives the problem.

Filling in the missing values and putting the field as required resolved the problem.

Ciao,

Bert