title: Will Django UUIDFIeld unique=True, blank=True and null=True behave correctly?
body: <p>I am adding a field to a database:</p>
  
  <p><code>identifier = models.UUIDField(unique=True, null=True, blank=True)</code></p>
  
  <p>but I am curious if this will behave like a CharField or a number field when someone saves an instance in the admin without a value. Will it try to save the value as an empty string <code>""</code> or will it be smart and save it as <code>null</code>? I am using Postgres for the database. I've seen other <a href="https://stackoverflow.com/questions/8609192/differentiate-null-true-blank-true-in-django">answers for CharField</a>, but nothing that speaks to UUIDField. </p>
  
  <p>My end goal is to have a field that is guaranteed to be unique, and will default to <code>null</code>. would it be more appropriate to write it as:</p>
  
  <p><code>identifier = models.UUIDField(unique=True, null=True, default=None)</code> or will the admin form validation complain if no value is provided?</p>