escape undefined to empty string

app/components.js

@@ -39,7 +39,9 @@ handlebars.registerHelper('n', function(object){
 // escapes so that the object can go in a double quote (") string
 handlebars.registerHelper('e', function(object){
   let s = stringify(object)
-  if (!s.startsWith('"'))
+  if (s === undefined)
+    s = '""'
+  else if (!s.startsWith('"'))
     s = stringify(s)
   return new handlebars.SafeString(s.slice(1, s.length-1))
 });