From 88f4beb08faf7e9849c45ad5a8166bca7bdbc248 Mon Sep 17 00:00:00 2001
From: dgtlmoon <dgtlmoon@gmail.com>
Date: Tue, 5 May 2026 20:32:14 +1000
Subject: [PATCH] Notifications - extra check for system default #4119 (#4122)

---
 changedetectionio/notification/handler.py    |  3 ++
 changedetectionio/notification_service.py    |  6 ++--
 changedetectionio/tests/test_notification.py | 33 ++++++++++++++++++++
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/changedetectionio/notification/handler.py b/changedetectionio/notification/handler.py
index 5e664d03..a5f870af 100644
--- a/changedetectionio/notification/handler.py
+++ b/changedetectionio/notification/handler.py
@@ -65,6 +65,9 @@ def notification_format_align_with_apprise(n_format : str):
     :return:
     """
 
+    if not n_format:
+        return NotifyFormat.TEXT.value
+
     if n_format.startswith('html'):
         # Apprise only knows 'html' not 'htmlcolor' etc, which shouldnt matter here
         n_format = NotifyFormat.HTML.value
diff --git a/changedetectionio/notification_service.py b/changedetectionio/notification_service.py
index c812b1d9..13f3f2d7 100644
--- a/changedetectionio/notification_service.py
+++ b/changedetectionio/notification_service.py
@@ -29,7 +29,7 @@ def _check_cascading_vars(datastore, var_name, watch):
     v = watch.get(var_name)
     if v and not watch.get('notification_muted'):
         if var_name == 'notification_format' and v == USE_SYSTEM_DEFAULT_NOTIFICATION_FORMAT_FOR_WATCH:
-            return datastore.data['settings']['application'].get('notification_format')
+            return datastore.data['settings']['application'].get('notification_format') or default_notification_format
 
         return v
 
@@ -457,7 +457,7 @@ Thanks - Your omniscient changedetection.io installation.
             'notification_body': body,
             'notification_format': _check_cascading_vars(self.datastore, 'notification_format', watch),
         })
-        n_object['markup_text_links_to_html_links'] = n_object.get('notification_format').startswith('html')
+        n_object['markup_text_links_to_html_links'] = (n_object.get('notification_format') or '').startswith('html')
 
         if len(watch['notification_urls']):
             n_object['notification_urls'] = watch['notification_urls']
@@ -506,7 +506,7 @@ Thanks - Your omniscient changedetection.io installation.
             'notification_body': body,
             'notification_format': _check_cascading_vars(self.datastore, 'notification_format', watch),
         })
-        n_object['markup_text_links_to_html_links'] = n_object.get('notification_format').startswith('html')
+        n_object['markup_text_links_to_html_links'] = (n_object.get('notification_format') or '').startswith('html')
 
         if len(watch['notification_urls']):
             n_object['notification_urls'] = watch['notification_urls']
diff --git a/changedetectionio/tests/test_notification.py b/changedetectionio/tests/test_notification.py
index a679485f..0b9e6daf 100644
--- a/changedetectionio/tests/test_notification.py
+++ b/changedetectionio/tests/test_notification.py
@@ -541,6 +541,39 @@ def test_single_send_test_notification_on_watch(client, live_server, measure_mem
         assert 'Current snapshot: Example text: example test' in x
     os.unlink(os.path.join(datastore_path, "notification.txt"))
 
+# Regression test for #4119 - sending a test notification with 'System default' format caused a crash
+def test_send_test_notification_with_system_default_format(client, live_server, measure_memory_usage, datastore_path):
+
+    set_original_response(datastore_path=datastore_path)
+    if os.path.isfile(os.path.join(datastore_path, "notification.txt")):
+        os.unlink(os.path.join(datastore_path, "notification.txt"))
+
+    test_notification_url = url_for('test_notification_endpoint', _external=True).replace('http://', 'post://') + "?status_code=204"
+
+    test_url = url_for('test_endpoint', _external=True)
+    uuid = client.application.config.get('DATASTORE').add_watch(url=test_url)
+    client.get(url_for("ui.form_watch_checknow"), follow_redirects=True)
+    wait_for_all_checks(client)
+
+    # New watches default to USE_SYSTEM_DEFAULT_NOTIFICATION_FORMAT_FOR_WATCH.
+    # The JS sends this value verbatim from the select; it must not crash.
+    res = client.post(
+        url_for("ui.ui_notification.ajax_callback_send_notification_test") + f"/{uuid}",
+        data={
+            "notification_urls": test_notification_url,
+            "notification_body": default_notification_body,
+            "notification_title": default_notification_title,
+            "notification_format": USE_SYSTEM_DEFAULT_NOTIFICATION_FORMAT_FOR_WATCH,
+        },
+        follow_redirects=True
+    )
+
+    assert res.status_code != 400
+    assert res.status_code != 500
+
+    client.get(url_for("ui.form_delete", uuid="all"), follow_redirects=True)
+
+
 def _test_color_notifications(client, notification_body_token, datastore_path):
 
     set_original_response(datastore_path=datastore_path)