Unproper warning thrown with event handler invoke with async error handling

[AlexandreBonaventure]

Version

2.6.0

Reproduction link

https://jsfiddle.net/jk8as0bz/

Steps to reproduce

NB: use a component with a transpiled render function (render._withStripped should be true). For the purpose of the minimal repro, we are setting the flag manually.

on the minimal repro open the console, click on the button and see the warning message showing up

What is expected?

no warning

What is actually happening?

it throws an improper warning

---

What is happening

1. create a component that $emit directly in an event handler like <button @click="$emit('click')">click me! </button>
2. The handler will be compiled as such in the createElement function

on: {
                click: function($event) {
                  return _vm.$emit("closeModal")
                }
}

returning the vm instance
3. In the isPromise call it will check for property like .then or .catch
4. the withStriped flag set to true the vm instance is proxied to throw non present properties but referenced during render on development
5. It will throw the following warning: [Vue warn]: Property or method "then" is not defined on the instance but referenced during render

[AlexandreBonaventure]

Ho someone just reported the bug 15 minutes before. #9418
sorry for the duplicate