Firebase App named '[DEFAULT]' already exists (app/duplicate-app). for meta version 9 code example

Example 1: Firebase: Firebase App named '[DEFAULT]' already exists (app/duplicate-app).

if (!firebase.apps.length) {
    firebase.initializeApp({});
}

Example 2: Firebase: Firebase App named '[DEFAULT]' already exists (app/duplicate-app).

if (!firebase.apps.length) {
    firebase.initializeApp(firebaseConfig);
}