fix cascade club

tournaments/models/event.py

@@ -4,7 +4,7 @@ import uuid
 
 class Event(models.Model):
     id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=True)
-    club = models.ForeignKey(Club, on_delete=models.CASCADE, null=True, blank=True)
+    club = models.ForeignKey(Club, on_delete=models.SET_NULL, null=True, blank=True)
     creation_date = models.DateTimeField()
     creator = models.ForeignKey(CustomUser, blank=True, null=True, on_delete=models.CASCADE)
     name = models.CharField(max_length=200, null=True, blank=True)