Fixed #23617 -- Added get_pk_value_on_save()

The method is mainly intended for use with UUIDField. For UUIDField we
want to call the field's default even when primary key value is
explicitly set to None to match the behavior of AutoField.

Thanks to Marc Tamlyn and Tim Graham for review.

django/db/models/query.py

@@ -398,6 +398,11 @@ class QuerySet(object):
         obj.save(force_insert=True, using=self.db)
         return obj
 
+    def _populate_pk_values(self, objs):
+        for obj in objs:
+            if obj.pk is None:
+                obj.pk = obj._meta.pk.get_pk_value_on_save(obj)
+
     def bulk_create(self, objs, batch_size=None):
         """
         Inserts each of the instances into the database. This does *not* call
@@ -422,6 +427,8 @@ class QuerySet(object):
         self._for_write = True
         connection = connections[self.db]
         fields = self.model._meta.local_concrete_fields
+        objs = list(objs)
+        self._populate_pk_values(objs)
         with transaction.atomic(using=self.db, savepoint=False):
             if (connection.features.can_combine_inserts_with_and_without_auto_increment_pk
                     and self.model._meta.has_auto_field):