Firebase error: (app/invalid-app-argument) in react native

When I run this code (react native), the following error appears:

FirebaseError: Firebase: firebase.database() takes either no argument or a Firebase App instance. (app/invalid-app-argument).

Here's the code (when I run the similar code in other files(inside the same project) works perfectly):

import React from "react";
import { View, Text } from "react-native";
import * as firebase from "firebase";

class screen extends React.Component {

  componentDidMount() {
    firebase.auth().onAuthStateChanged((user) => {
      if (user) {
        firebase
          .database()
          .ref("users/" + user.uid + "/keys")
          .on("value", function (snapshot) {
            console.log(snapshot.val()); //works
            snapshot.forEach(function (childSnapshot) {
              console.log("hello"); //works
              var key = childSnapshot.val();
              firebase
                .database("users/" + key + "/whatever")
                .on("value", function (snapshot) {
                  console.log(snapshot.val()); //Doesn't work
                });
            });
          });
      }
    })
  }

  render() {
    return (
      <View>
       <Text>Hello</Text>
      </View>
    );
  }
}

export default screen;