ctx.body happens with nothing, even though console.log works.
I am using mongoose for my database, and below is a controller function which shows the list of posts.

```
export const list = async ctx => {
	try {
		Post.find().exec().then(posts => {
                       // works (shows three posts)
			console.log(posts);
                       // not work (shows nothing)
			ctx.body = posts;
		});
	} catch (e) {
		ctx.status(500, e);
	}
}
```

It obviously works with async function.

```
export const list = async ctx => {
	try {
		    await posts = Post.find().exec();
                   // works fine
		    ctx.body = posts;
		});
	} catch (e) {
		ctx.status(500, e);
	}
}
```

What is wrong with that first example code? 

console.log works fine, but ctx.body happens to nothing.

What am I misunderstading?
