How to get the email out of the AuthCredential object with Android?

Question

I have a method with which I sign in with Facebook:

void signInWithFB(AuthCredential fbCredential) {
    //How to get the the email out off fbCredential object???
    //                              IS RED
    auth.fetchSignInMethodsForEmail(email).addOnCompleteListener(task -> {
        if (task.isSuccessful()) {
            auth.signInWithCredential(fbCredential).addOnCompleteListener(t -> {
                if (t.isSuccessful()) {
                    //Do some stuff
                } else {
                    Lod.d("APP_TAG", t.getException().getMessage());
                }
            });
        }
    });
}

I tried to use:

String email = fbCredential.getProvider().getEmail();

But there is no such a function. How can I get the email address out of the fbCredential, So I check out if it already exists?