[BUG] create helper function ignores the id property when it's equal to 0.

Description :
Create call on a loopback model returns a property id as a response, in case where the property id starts from 0 it is removed from response. This is because the create function( dao.js line no 378) which gets the id as a callback on the create call in a loopback model, does not accepts 0 as an id.

Code snippet from dao.js
if id is 0 it is skipping the if block

function createCallback(err, id, rev) {          
if (id) {
  obj.__data[_idName] = id;
   defineReadonlyProp(obj, _idName, id);
}

We have a scenario where the id starts from 0, and this is causing the id property for our 0th element to be removed from the response.

Steps to reproduce :

• Model which has a property id which starts from 0.
• Call the api to create which will have the id (starting from 0) in response.
• Response will be missing the id property for the first call where id is 0, and it'll add the id property in response starting from id as 1 onwards.

Current Response Behaviour :
id is removed when its value is equal to 0

{
    "property1" : "property1",
   "property2" : "property2"
}

Expected Results :

{
    "id" : 0
    "property1" : "property1",
    "property2" : "property2"
}

Beginne bei der Funktion createCallback in dao.js ungefähr bei Zeile 378 und verfolge, wie die Callback-ID dem erstellten Objekt zugewiesen wird. Reproduziere einen create-Aufruf mit einer ID von 0, füge anschließend eine Testabdeckung für die erwartete Antwort hinzu und überprüfe, dass IDs von 0 und höher beibehalten werden.