protected function _setEmailSingle($varName, $email, $name, $throwMessage)
    {
        if ($email === []) {
            $this->{$varName} = $email;

            return $this;
        }

        $current = $this->{$varName};
        $this->_setEmail($varName, $email, $name);
        if (count($this->{$varName}) !== 1) {
            $this->{$varName} = $current;
            throw new InvalidArgumentException($throwMessage);
        }

        return $this;
    }