Idle session time out error is not intuitive to end users

If Nintex new responsive forms on O365 is idle for a long time, the session times out in the background. However after the user has filled all the fields in the form and he hits Submit button, the alert appears "Unable to Save. Object reference not set to an instance of an object." This is super confusing to the end users. If this alert can have a simple message like "As your form was idle since a long time, your session has timed out." We should show this. However before this a count down ticker should come on top of the form with a pop-up stating the session will time out in X mins, please click Yes to continue the session." This will be even better as some forms are long/lengthy and we should give a warning to the end user that the session is timing out soon.