Issue
After importing a Subscription license (.nlfx) from an Expiring license (.nlf), some workflows are unable to be open in the Nintex Workflow Designer.
Error Code
System.NullReferenceException: Object reference not set to an instance of an object.
at Nintex.Workflow.ApplicationPages.Preview.IsWorkflowProduction()
at Nintex.Workflow.ApplicationPages.Preview.Page_Load(Object sender, EventArgs e)
at System.EventHandler.Invoke(Object sender, EventArgs e)
at System.Web.UI.Control.OnLoad(EventArgs e)
at Microsoft.SharePoint.WebControls.UnsecuredLayoutsPageBase.OnLoad(EventArgs e)
at Microsoft.SharePoint.WebControls.LayoutsPageBase.OnLoad(EventArgs e)
at Nintex.Workflow.ServerControls.NintexLayoutsBase.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Resolution
Update to the March 2020 release or later for each respective version of SharePoint. The March 2020 versions are as follows:
Nintex Workflow for SharePoint 2013 - 3.5.2.0
Nintex for SharePoint 2016 - 4.5.2.0
Nintex for SharePoint 2019 - 5.1.2.0
Additional Information
This issue is not explicitly mentioned in the release notes, however, the March 2020 release is the only release that has any mention of addressing an issue when moving from perpetual to subscription licensing:
"Fixed issue where workflow and actions not calculated when importing subscription license from perpetual license (163904)"
It is also possible that the null reference is in regard to a user that no longer exists. If the only workflows impacted by this issue were last published by a non-existent account, and there are not many workflows to fix, it may be worth simply exporting, importing, and publishing the workflows again.
Related Links
Updating Workflow and Forms for SharePoint On-Premises
Release Notes
https://help.nintex.com/en-US/platform/ReleaseNotes.htm
