I have a text field called
GIS_ID which I would like to populate with a unique UUID only if it doesn't have a valid UUID already. That is, if the field is NULL, or contains any other value other than a valid UUID, then I want it to populate it with a UUID. If there is already a valid UUID in the field, then I want it to do nothing.
I'm using ArcGIS Desktop 10.4.1 Standard License and I want to populate the field using the field calculator. I'm also aware of GUID Fields in ArcGIS but they aren't suitable for the client's purposes.