--- a/mercurial/templatefilters.py	Sun Apr 02 11:46:49 2017 +0900
+++ b/mercurial/templatefilters.py	Sun Apr 02 11:51:25 2017 +0900
@@ -219,8 +219,12 @@
 
 @templatefilter('json')
 def json(obj):
-    if obj is None or obj is False or obj is True:
-        return {None: 'null', False: 'false', True: 'true'}[obj]
+    if obj is None:
+        return 'null'
+    elif obj is False:
+        return 'false'
+    elif obj is True:
+        return 'true'
     elif isinstance(obj, (int, long, float)):
         return str(obj)
     elif isinstance(obj, str):