[fix] engines: base URL can be a list or a string, but its not None!

The code injection and monkey patching examine the names in the module of the
engine; if a variable there starts without an underscore and has the value None,
then this variable needs to be configured. This outdated concept does not fit
engines that may have multiple URLs. At least not as long as the value of the
base URL (list) is None.

The default is now an empty list instead of None

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

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(_):

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

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):

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.
 """