diff --git a/searx/engines/invidious.py b/searx/engines/invidious.py
index 817c1d4ab..c62143ffc 100644
--- a/searx/engines/invidious.py
+++ b/searx/engines/invidious.py
@@ -31,7 +31,7 @@ paging = True
 time_range_support = True
 
 # base_url can be overwritten by a list of URLs in the settings.yml
-base_url: list | str = []
+base_url: list[str] | str = []
 
 
 def init(_):
diff --git a/searx/engines/piped.py b/searx/engines/piped.py
index 564753494..e9585eae1 100644
--- a/searx/engines/piped.py
+++ b/searx/engines/piped.py
@@ -72,7 +72,7 @@ categories = []
 paging = True
 
 # search-url
-backend_url: list[str] | str | None = None
+backend_url: list[str] | str = []
 """Piped-Backend_: The core component behind Piped.  The value is an URL or a
 list of URLs.  In the latter case instance will be selected randomly.  For a
 complete list of official instances see Piped-Instances (`JSON
diff --git a/searx/engines/pixiv.py b/searx/engines/pixiv.py
index abf316228..b1e7bf452 100644
--- a/searx/engines/pixiv.py
+++ b/searx/engines/pixiv.py
@@ -20,7 +20,7 @@ categories = ['images']
 
 # Search URL
 base_url = "https://www.pixiv.net/ajax/search/illustrations"
-pixiv_image_proxies: list = []
+pixiv_image_proxies: list[str] = []
 
 
 def request(query, params):
diff --git a/searx/engines/yacy.py b/searx/engines/yacy.py
index e8ba1292a..6566dd0f6 100644
--- a/searx/engines/yacy.py
+++ b/searx/engines/yacy.py
@@ -96,7 +96,7 @@ search_type = 'text'
 ``video`` are not yet implemented (Pull-Requests are welcome).
 """
 
-base_url: list[str] | str | None = None
+base_url: list[str] | str = []
 """The value is an URL or a list of URLs.  In the latter case instance will be
 selected randomly.
 """