Added an additional check to ensure that unique field restrictions don't honor null values.
Fixes #4041 (closed)
developcreate a new form with a single line text field that is the form's unique field.
- Submit the form with nothing in the field.
- If you try to resubmit, there will be a unique field error on the empty field.
- Checkout this branch.
- If you try to resubmit the form, there will not be a unique field error on the empty field.