Support '' as the argument for the setlocale emulation. Fixes #678259.
diff --git a/Lib/locale.py b/Lib/locale.py
index 3551261..2028948 100644
--- a/Lib/locale.py
+++ b/Lib/locale.py
@@ -69,7 +69,7 @@
         """ setlocale(integer,string=None) -> string.
             Activates/queries locale processing.
         """
-        if value is not None and value != 'C':
+        if value not in (None, '', 'C'):
             raise Error, '_locale emulation only supports "C" locale'
         return 'C'