javascript - Google Firebase Error(Function returned undefined, expected Promise or value)

Question

I'm developing Server with Firebase.

I had copied Google Developer's Video on Youtube.

It works well, but on log there is an error:

Function returned undefined, expected Promise or value

It says function returned undefined, but I make function return a promise `set``

How can I solve this?

function sanitize(s) {
    var sanitizedText = s;
    console.log('sanitize params: ', sanitizedText);
    sanitizedText = sanitizedText.replace(/stupid/ig, "wonderful");
    return sanitizedText;
}
exports.sanitizePost = functions.database
    .ref('/posts/{pushId}')
    .onWrite(event => {
        const post = event.data.val();
        if (post.sanitized) return;

        console.log('Sanitizing new post', event.params.pushId);
        console.log(post);
        post.sanitized = true;
        post.title = sanitize(post.title);
        post.body = sanitize(post.body);
        return event.data.ref.set(post); 
    })

I'm beginner of Firebase, Nodejs.

Answer 1

Waitting for answers