I am quite new in react native and found simple solution from tutorial for fetching&loading case

export const useFetching = (callback) => {
    const [isLoading, setIsLoading] = useState(false);
    const [error, setError] = useState('');

    const fetching = async(data) => {
        try{
            setIsLoading(true);
            await callback(data);
        } catch(e) {
            setError(e.message);
        } finally {
            setIsLoading(false);
        }
    }
    return [fetching, isLoading, error];
}

I use it with signUp func from react-navigation docs as a callback, which is supposed to change the screen to main app:

signIn: async (data) => {
    const token = await AuthManager.login(data);
    if (token)
        dispatch({ type: 'SIGN_IN', token: 'dummy-auth-token' });

But when I call it I get "Can't perform a React state update on an unmounted component". I found out that:

1. The "finally" block from useFetching causes the error
2. Empty useEffect useEffect(() => {return () => {}},[]) inserted into login screen removes the problem

I'm wondering, is there any normal solution in this case and why useEffect helps here?