code: public final GoogleAccountCredential setSelectedAccountName(String accountName) {
      selectedAccount = accountManager.getAccountByName(accountName);
      // check if account has been deleted
      this.accountName = selectedAccount == null ? null : accountName;
      return this;
    }
docs: Sets the selected Google account name (e-mail address) -- for example
  {@code "johndoe@gmail.com"} -- or {@code null} for none.