diff --git a/gallery_dl/extractor/common.py b/gallery_dl/extractor/common.py
index 719fc62c..568f435a 100644
--- a/gallery_dl/extractor/common.py
+++ b/gallery_dl/extractor/common.py
@@ -462,7 +462,7 @@ class Extractor():
                 headers["Referer"] = self.root + "/"
 
         custom_ua = self.config("user-agent")
-        if custom_ua is None or custom_ua == "auto":
+        if not custom_ua or custom_ua == "auto":
             pass
         elif custom_ua == "browser":
             headers["User-Agent"] = _browser_useragent(None)