We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
cannot delete user in django admin if user has not uploaded avatar 


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `euth/users/signals.py`
Content:
```
1 from django.db.models import signals
2 from django.dispatch import receiver
3 
4 from adhocracy4.images import services
5 
6 from . import models
7 
8 
9 @receiver(signals.post_init, sender=models.User)
10 def backup_image_path(sender, instance, **kwargs):
11     instance._current_image_file = instance.avatar
12 
13 
14 @receiver(signals.post_save, sender=models.User)
15 def delete_old_image(sender, instance, **kwargs):
16     if hasattr(instance, '_current_image_file'):
17         if instance._current_image_file != instance.avatar:
18             services.delete_images([instance._current_image_file])
19 
20 
21 @receiver(signals.post_delete, sender=models.User)
22 def delete_images_for_User(sender, instance, **kwargs):
23     services.delete_images([instance.avatar])
24
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/euth/users/signals.py b/euth/users/signals.py
--- a/euth/users/signals.py
+++ b/euth/users/signals.py
@@ -20,4 +20,4 @@
 
 @receiver(signals.post_delete, sender=models.User)
 def delete_images_for_User(sender, instance, **kwargs):
-    services.delete_images([instance.avatar])
+    services.delete_images([instance._avatar])

{"golden_diff": "diff --git a/euth/users/signals.py b/euth/users/signals.py\n--- a/euth/users/signals.py\n+++ b/euth/users/signals.py\n@@ -20,4 +20,4 @@\n \n @receiver(signals.post_delete, sender=models.User)\n def delete_images_for_User(sender, instance, **kwargs):\n-    services.delete_images([instance.avatar])\n+    services.delete_images([instance._avatar])\n", "issue": "cannot delete user in django admin if user has not uploaded avatar \n\n", "before_files": [{"content": "from django.db.models import signals\nfrom django.dispatch import receiver\n\nfrom adhocracy4.images import services\n\nfrom . import models\n\n\n@receiver(signals.post_init, sender=models.User)\ndef backup_image_path(sender, instance, **kwargs):\n    instance._current_image_file = instance.avatar\n\n\n@receiver(signals.post_save, sender=models.User)\ndef delete_old_image(sender, instance, **kwargs):\n    if hasattr(instance, '_current_image_file'):\n        if instance._current_image_file != instance.avatar:\n            services.delete_images([instance._current_image_file])\n\n\n@receiver(signals.post_delete, sender=models.User)\ndef delete_images_for_User(sender, instance, **kwargs):\n    services.delete_images([instance.avatar])\n", "path": "euth/users/signals.py"}], "after_files": [{"content": "from django.db.models import signals\nfrom django.dispatch import receiver\n\nfrom adhocracy4.images import services\n\nfrom . import models\n\n\n@receiver(signals.post_init, sender=models.User)\ndef backup_image_path(sender, instance, **kwargs):\n    instance._current_image_file = instance.avatar\n\n\n@receiver(signals.post_save, sender=models.User)\ndef delete_old_image(sender, instance, **kwargs):\n    if hasattr(instance, '_current_image_file'):\n        if instance._current_image_file != instance.avatar:\n            services.delete_images([instance._current_image_file])\n\n\n@receiver(signals.post_delete, sender=models.User)\ndef delete_images_for_User(sender, instance, **kwargs):\n    services.delete_images([instance._avatar])\n", "path": "euth/users/signals.py"}]}