I wonder if Nintex could at some point improve exception handling in Nintex.Workflow.HumanApproval. It is very fragile in the cases when some of the users don't have an email address specified. Maybe other things might cause this as well, but here's what I found.
Such things happen:
12-02-2015 20:13:20.42 w3wp.exe (0x9168) 0x900C SharePoint Foundation Legacy Workflow Infrastructure 88xr Unexpected WinWF Internal Error, terminating workflow Id# 73dd459d-5a1e-4dfb-96b0-07f1a8423775
12-02-2015 20:13:20.43 w3wp.exe (0x9168) 0x900C SharePoint Foundation Legacy Workflow Infrastructure 98d4 Unexpected System.NullReferenceException: Object reference not set to an instance of an object. at TBs=.LRw=.Mhw=(NWContextDataCollection Mxw=, Approver NBw=, NWWorkflowContext NRw=, ContextDataOptions Nhw=, Boolean Nxw=) at Nintex.Workflow.HumanApproval.Message.Send(Approver approver, Message persistTo) at Nintex.Workflow.HumanApproval.MultiOutcomeTask.ClosePendingApprovers(Boolean informPendingApprovers, Outcome reason, UpdateApproverTaskMode closureMethod) at Nintex.Workflow.Activities.AssignTodoTaskInternal.TaskCompleted(Object sender, EventArgs e) at System.Workflow.ComponentModel.Activity.RaiseEvent(DependencyProperty dependencyEvent, Object sender, EventArgs e) at System.Workflow.Activities.ReplicatorActivity.Cancel(ActivityExecutionContext executionContext) at System.Workflow.ComponentModel.CompositeActivity.HandleFault(ActivityExecutionContext executionContext, Exception exception) at System.Workflow.ComponentModel.ActivityExecutor`1.HandleFault(T activity, ActivityExecutionContext executionContext, Exception exception) at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime) at System.Workflow.Runtime.Scheduler.Run()
Or should I cross post this to UserVoice?