I am trying to update a text field with the owner's name everytime the owner is changed to  one among a particular group of users. The new record's owner id is correctly returned in the debug log however the rec.owner.Name is returning null. 

Can somebody help me understand what is the issue?

I am trying to update a text field with the owner's name everytime the owner is changed to  one among a particular group of users. The new record's owner id is correctly returned in the debug log however the rec.owner.Name is returning null. 

Can somebody help me understand what is the issue?