Handlebars:
Template
{{#with city}}
{{city.name}} (not shown because there is no city)
{{else}}
No city found
{{/with}}
Preparation-Script
// Handlebars.registerHelper('loud', function(string) {
//    return string.toUpperCase()
// });
Input
{
  person: {
    firstname: "Yehuda",
    lastname: "Katz",
  },
}
Output
No city found