Set service FK to null when it gets deleted

src/users/models/login.py

@@ -14,7 +14,7 @@ class Login(models.Model):
     description = models.TextField(blank=True)
     user = models.ForeignKey(User, on_delete=models.CASCADE)
     service = models.ForeignKey(
-        Service, on_delete=models.DO_NOTHING, blank=True, null=True
+        Service, on_delete=models.SET_NULL, blank=True, null=True
     )
     groups = models.ManyToManyField(Group, through="LoginInGroup")