getEmailProviderAdminEmail() {
    const emailSignInOption = this.getSignInOptionsForProvider_(
        firebase.auth.EmailAuthProvider.PROVIDER_ID);
    return (emailSignInOption && emailSignInOption['disableSignUp'] &&
            emailSignInOption['disableSignUp']['adminEmail']) || null;
  }
@return {?string} The admin contact email when sign up is disabled.