Postcode search button on homepage lacks empty/null validation

[djohnstonCC]

Clicking on the postcode search button displayed on the home page results in an attempted search and redirect to 'Sorry, doesn't appear to be a valid postcode.' page, even if postcode input element is left blank. May be kinder to users to provide a validation prompt on the home screen ('Please input a postcode'), rather than transitioning to an error screen.