Returning 'undefined' from function of a service causes an error

[gear54rus]

This one:

2016-01-12 09:19:37.098 [ERROR][R:08f961] Unknown error while trying to pass the request to instance: TypeError: Cannot read property 'then' of undefined
    at Instance.handleRequest (../../_src/runtime/instance.js:529:28)
    at Endpoint.handleRequest (../../_src/runtime/endpoint.js:483:21)
    at ../../_src/runtime/router.js:347:21
    at Router._handleRequest (../../_src/runtime/router.js:348:8)
    at Server.<anonymous> (../../_src/runtime/router.js:197:14)
    at emitTwo (events.js:87:13)
    at Server.emit (events.js:172:7)
    at HTTPParser.parserOnIncoming [as onIncoming] (_http_server.js:529:12)
    at HTTPParser.parserOnHeadersComplete (_http_common.js:88:23)

If undefined is returned, it shouldn't even bother with checking if it's a promise.