If appName field is completely missing from config file, playground hangs without error message

[pharaxe]

Versions

angular-playground version 3.4.0

Output from: ng --version:

Angular CLI: 1.6.0
Node: 9.2.1
OS: linux x64
Angular: 

Output from: npm --version

5.6.0

Repro steps

• Download a fresh copy of Angular Playground and set up the cli-example
• cd examples/cli-example
• npm i
• delete the line that has the appName configuration option in angular-playground.json
• Try starting playground
• npm run playground

Observed Behavior

Hangs without any message

$ npm run playground

> cli-example@0.0.0 playground /var/www/html/angular-playground/examples/cli-example
> node ./node_modules/angular-playground/dist/bin/index.js

Successfully compiled sandbox files.

Desired Behavior

$ npm run playground

> cli-example@0.0.0 playground /var/www/html/angular-playground/examples/cli-example
> node ./node_modules/angular-playground/dist/bin/index.js

Successfully compiled sandbox files.
Please provide Playground's appName in your angular-playground.json file.

Details

This is basically the same issue as #93, where a thrown error doesn't surface to the user. I don't think it's as important a bug because in the case where appName is present but misspelled there is a error message. Only when the appName field is completely missing from the config file does this happen.