blueprints: fix error when entry with state absent doesn't exist

closes #4305

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

authentik/blueprints/tests/fixtures/state_absent.yaml

@@ -5,3 +5,9 @@ entries:
           slug: "%(id)s"
       model: authentik_flows.flow
       state: absent
+    - identifiers:
+          name: "%(id)s"
+          expression: |
+            return True
+      model: authentik_policies_expression.expressionpolicy
+      state: absent

authentik/blueprints/v1/importer.py

@@ -268,7 +268,7 @@ class Importer:
                 self.logger.debug("updated model", model=model)
             elif state == BlueprintEntryDesiredState.ABSENT:
                 instance: Optional[Model] = serializer.instance
-                if instance:
+                if instance.pk:
                     instance.delete()
                     self.logger.debug("deleted model", mode=instance)
                     continue