diff --git a/js/legacy/widgets/form/print_format.js b/js/legacy/widgets/form/print_format.js
index 66e89d5acb..fbe662430f 100644
--- a/js/legacy/widgets/form/print_format.js
+++ b/js/legacy/widgets/form/print_format.js
@@ -35,6 +35,7 @@ _p.go = function(html) {
 
 _p.preview = function(html) {
 	var w = window.open('');
+	if(!w) return;
 	w.document.write(html)
 	w.document.close();
 }
diff --git a/wnf.py b/wnf.py
index f9d8835971..131875b1f5 100755
--- a/wnf.py
+++ b/wnf.py
@@ -259,10 +259,16 @@ def run():
 	elif options.sync_all is not None:
 		import webnotes.model.sync
 		webnotes.model.sync.sync_all(options.force or 0)
+		# update js code version (clear to localStorage)
+		from build.project import update_version
+		update_version()
 
 	elif options.sync is not None:
 		import webnotes.model.sync
 		webnotes.model.sync.sync(options.sync[0], options.sync[1], options.force or 0)
+		# update js code version (clear to localStorage)
+		from build.project import update_version
+		update_version()
 
 	# print messages
 	if webnotes.message_log: