Error "System.ArgumentException: AssignedTo at System.Activities.Statements.Throw.Execute"

ISSUE

When running a workflow containing a Task action, the following error might occur:

ERROR CODE

Details: An unhandled exception occurred during the execution of the workflow instance.  Exception details: System.ArgumentException: AssignedTo at System.Activities.Statements.Throw.Execute(CodeActivityContext context) at System.Activities.CodeActivity.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager) at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation)  Exception from activity Throw If Sequence NintexActivities.WorkflowXaml_{GUID} [Task action name] 

RESOLUTION

From the Nintex Workflow for Office 365 Designer, specify the format value of field "Participant" as an "Email Address":

1. Drag action "Assign a task" or "Start a task process" into Workflow Designer.
2. Double-click the action to configure it. 
3. Navigate to field "Participants" and specify a value. 
4. Click the "fx" button beside the "Participants" value to specify the format of this value. 
5. Choose "Email Address" from the pop-up dialog window to choose how to format value of "Participant".