"System.ArgumentException: Argument 'file.Extension' may not be null or empty" when uploading a file without an extension using File Attachment control

  • 16 February 2021
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"System.ArgumentException: Argument 'file.Extension' may not be null or empty" when uploading a file without an extension using File Attachment control


K2 blackpearl 4.7
K2 4.7 March 2018 Cumulative Update
K2 blackpearl 4.7
This article was created in response to a support issue logged with K2. The content may include typographical errors and may be revised at any time without notice. This article is not considered official documentation for K2 software and is provided "as is" with no warranties.
This article has been archived, and/or refers to legacy products, components or features. The content in this article is offered "as is" and will no longer be updated. Archived content is provided for reference purposes only. This content does not infer that the product, component or feature is supported, or that the product, component or feature will continue to function as described herein.


When attempting to upload a file without an extension using the File Attachment control causes exception and a restart of the SmartForms application pool.


You may see Event ID 1325 of Error Level logged in Application log with the following details:

FileUtility.StoreFileToRemoteServer(File=FileNameWithoutExtension, Hash=2B5CC1B9357729EC5731B01611E70275). Exception: System.ArgumentException: Argument 'file.Extension' may not be null or empty Parameter name: file.Extension at SourceCode.Forms.Management.ThrowHelper.ArgumentNullOrEmpty(String parameterName) at SourceCode.Forms.Management.FormsManager.SetFile(FileInfo file) at SourceCode.Forms.AppFramework.FileUtility.StoreFileToRemoteServer(FileInfo file, Stream stream, Int32 fileLength)

Log Name: Application
Event ID: 1325
Level: Error
Source: ASP.NET 4.0.30319.0

Sample error message screenshot:




This is a known issue which has been addressed in K2 4.7 March 2018 Cumulative Update Fix Pack 38.


Without FP38 installed, attempting to upload a file without an attachment is blocked. When you select the file, you receive a "File not uploaded. Details." error message, with the following explanation available after clicking on Details: "The file attachment has no extension. Select a file with a valid extension."

This prevents an unhandled exception of the IIS application pool. A possible workaround which can be used until FP38 is not installed, is to use an extensions blacklist. You just need to put 2 commas (",,") into the Runtime web.config as Forms.Designer.Controls.Attachment.Blacklist value, i.e:

<add key="Forms.Designer.Controls.Attachment.Blacklist" value=",," />
No IIS restart is required after this change. With this setting in place and without FP38 installed an attempt to upload a file without extension, the following message is presented to the user:
%FileName% File not uploaded Details.
Details: This type of file may not be attached.

Sample message screenshot:


This also prevents unhandled exceptions. In addition to this, in control properties there is an Allowed Types property which allows you to specify a limited set of allowed extensions which will dictate what will be targeted by Windows Explorer open file dialog (i.e. it will be showing only those file extensions by default), though user still can change this in the drop-down. Use of this setting greatly reduces the possibility of uploading a file with no extension by accident.

It also adds a "Valid extensions are:" line which lists allowed extensions to the error message details:


You may also consider adding a data label with red text instructing users to upload only specific extensions if necessary:


The recommended resolution is to download and install the appropriate update:

For K2 4.7 - K2 4.7 March 2018 Cumulative Update Fix Pack 38 or newer. See KB002967 for details.
For K2 5.0 - Upgrade to newer versions of K2 listed below.
For K2 5.1 - K2 Five (5.1) November 2018 Cumulative Update Fix Pack 7. See KB002969 for details.
For K2 5.2 - K2 Five (5.2) Fix Pack 21 or newer. See KB002973 for details.

When applying updates it is not possible use workarounds mentioned above to resolve this issue.

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