Google Cloud Function undefined argument detected as null

Question

When I pass an undefined argument to my cloud function, it is detected as null. For example, if I have this:

 const a = undefined;

 firebase.functions().httpsCallable("myFunction")({
    a
 });

And in my cloud function I do:

...
.https.onCall(async (data, context) => {

    const {a} = data;

    console.log(a);

    ...
});

It prints "null" and not "undefined".

myFunction: null

Why?

user_8682941 · Answer

When you call your remote function, the payload (ie. your data) is serialized:

The first operation Serializer does (for each property) is:

if (data == null) {
   return null;
}

Since == is used in lieu of ===, undefined is turned into null.