How to stop a custom field being edited to blank?

[Kirsty Mcloughlin]

On one of create screens we have a mandatory field called 'Project Manager' which is a user picker field.

We have found however, that people are later deleting their name out of this field, leaving it blank which is bottle-necking our process.

How do I implement it so that if someone tries to remove their name from this field then an alternative name MUST be inserted and not left as blank?

[Salzi]

Remove the field from the edit screen and make it only editable in one tranistion to itself (with a separate mask for this) then you can then use a validation that checks whether the field is filled out.