--- a/mercurial/ui.py	Sun Jun 25 14:34:34 2017 +0200
+++ b/mercurial/ui.py	Sun Jun 25 14:38:56 2017 +0200
@@ -540,8 +540,10 @@
         ConfigError: foo.invalid is not a boolean ('somevalue')
         """
 
-        v = self.config(section, name, default, untrusted=untrusted)
+        v = self._config(section, name, default, untrusted=untrusted)
         if v is None:
+            return v
+        if v is _unset:
             if default is _unset:
                 return False
             return default