functions-samples: delete-unused-accounts-cron : TypeError: functions.https.onRequest(...).then is not a function

How to reproduce these conditions

Follow the readme :

• Create a Firebase Project using the Firebase Developer Console
• Download this sample e.g. git clone https://github.com/firebase/functions-samples
• Enter the sample directory cd functions-samples/delete-unused-accounts-cron
• Setup the sample with your project firebase use --add and follow the instructions.
• Install node dependencies of your Functions cd functions; npm install; cd -
• Deploy your project using firebase deploy.

Debug output

=== Deploying to 'project'...

i  deploying functions
i  functions: ensuring necessary APIs are enabled...
+  functions: all necessary APIs are enabled
i  functions: preparing functions directory for uploading...

Error: Error occurred while parsing your function triggers.

TypeError: functions.https.onRequest(...).then is not a function
    at Object.<anonymous> (functions-samples\delete-unused-accounts-cron\functions\index.js:47:4)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\lib\triggerParser.js:18:11
    at Object.<anonymous> (C:\Users\user\AppData\Roaming\npm\node_modules\firebase-tools\lib\triggerParser.js:38:3)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:393:7)
    at startup (bootstrap_node.js:150:9)
    at bootstrap_node.js:508:3```