message: Make sure 'publicUrl' is set.
diff: @@ -8,6 +8,10 @@ import routes from './routes';
  export default function(): Middleware {
  + if (process.env.PUBLIC_URI === undefined) {
  + throw new Error('A PUBLIC_URI environment variable');
  + }
  +
  const middlewares = [
  halBrowser({
  title: 'a12n-server',
  