diff --git a/yt_dlp/extractor/niconico.py b/yt_dlp/extractor/niconico.py
index 09c53f096e..1e530a5cc9 100644
--- a/yt_dlp/extractor/niconico.py
+++ b/yt_dlp/extractor/niconico.py
@@ -45,8 +45,8 @@ class NiconicoBaseIE(InfoExtractor):
     def is_logged_in(self):
         return bool(self._get_cookies('https://www.nicovideo.jp').get('user_session'))
 
-    def _raise_login_error(self, error, default, expected=True):
-        raise ExtractorError(f'Unable to login: {error or default}', expected=expected)
+    def _raise_login_error(self, message, expected=True):
+        raise ExtractorError(f'Unable to login: {message}', expected=expected)
 
     def _perform_login(self, username, password):
         if self.is_logged_in:
@@ -69,7 +69,7 @@ class NiconicoBaseIE(InfoExtractor):
         elif err_msg := traverse_obj(webpage, (
             {find_element(cls='notice error')}, {find_element(cls='notice__text')}, {clean_html},
         )):
-            self._raise_login_error(err_msg, 'Invalid username or password')
+            self._raise_login_error(err_msg or 'Invalid username or password')
         elif 'oneTimePw' in webpage:
             post_url = self._search_regex(
                 r'<form[^>]+action=(["\'])(?P<url>.+?)\1', webpage, 'post url', group='url')
@@ -82,15 +82,15 @@ class NiconicoBaseIE(InfoExtractor):
                 }))
             if 'error-code' in parse_qs(urlh.url):
                 err_msg = traverse_obj(mfa, ({find_element(cls='pageMainMsg')}, {clean_html}))
-                self._raise_login_error(err_msg, 'MFA session expired')
+                self._raise_login_error(err_msg or 'MFA session expired')
             elif 'formError' in mfa:
                 err_msg = traverse_obj(mfa, (
                     {find_element(cls='formError')}, {find_element(tag='div')}, {clean_html}))
-                self._raise_login_error(err_msg, 'MFA challenge failed')
+                self._raise_login_error(err_msg or 'MFA challenge failed')
             elif self.is_logged_in:
                 return
 
-        self._raise_login_error(None, 'Unexpected login error', expected=False)
+        self._raise_login_error('Unexpected login error', expected=False)
 
 
 class NiconicoIE(NiconicoBaseIE):