Issue

When closing a workflow in the HTML5 Workflow Designer, the following error appears:

"Object reference not set to an instance of an object"

Symptoms

The full error message is as follows:

Image

Troubleshooting Steps

The error can occur when the related Form still has references to a deleted workflow in the Form's rules. You should see them marked as red, indicating that they are no longer applicable. 

To resolve the issue, you will need to remove all references to the deleted workflow.