Magento – How to override a model in Magento 2

I want to override the model for an optional lastname.

di.xml:

<type name="Magento\Customer\Model\Address\AbstractAddress">
    <plugin name="aroundAddressValidation" type="Xxx\OptionalLastname\Plugin\Customer\Model\Address\AbstractAddress" sortOrder="10"/>
</type>

AddressAbstract.php:

    <?php

    namespace Xxx\OptionalLastname\Plugin\Customer\Model\Address;

    class AbstractAddress
    {
        protected $_directoryData = null;
        protected $_eavConfig;

        public function __construct(
        \Magento\Directory\Helper\Data $directoryData, \Magento\Eav\Model\Config $eavConfig
        )
        {
            $this->_directoryData = $directoryData;
            $this->_eavConfig = $eavConfig;
        }

        public function aroundValidate(
        \Magento\Customer\Model\Address\AbstractAddress $subject, callable $proceed)
        {

            $errors = [];
            if (!\Zend_Validate::is($subject->getFirstname(), 'NotEmpty')) {
                $errors[] = __('%fieldName is a required field.', ['fieldName' => 'firstname']);
            }

            //
            // if (!\Zend_Validate::is($this->getLastname(), 'NotEmpty')) {
            // $errors[] = __('%fieldName is a required field.', ['fieldName' => 'lastname']);
            // }

            if (!\Zend_Validate::is($subject->getStreetLine(1), 'NotEmpty')) {
                $errors[] = __('%fieldName is a required field.', ['fieldName' => 'street']);
            }

            if (!\Zend_Validate::is($subject->getCity(), 'NotEmpty')) {
                $errors[] = __('%fieldName is a required field.', ['fieldName' => 'city']);
            }

            if ($this->isTelephoneRequired()) {
                if (!\Zend_Validate::is($subject->getTelephone(), 'NotEmpty')) {
                    $errors[] = __('%fieldName is a required field.', ['fieldName' => 'telephone']);
                }
            }

            if ($this->isFaxRequired()) {
                if (!\Zend_Validate::is($subject->getFax(), 'NotEmpty')) {
                    $errors[] = __('%fieldName is a required field.', ['fieldName' => 'fax']);
                }
            }

            if ($this->isCompanyRequired()) {
                if (!\Zend_Validate::is($subject->getCompany(), 'NotEmpty')) {
                    $errors[] = __('%fieldName is a required field.', ['fieldName' => 'company']);
                }
            }

            return $errors;
        }

        /**
         * @return bool
         * @since 100.2.0
         */
        protected function isCompanyRequired()
        {
            return ($this->_eavConfig->getAttribute('customer_address', 'company')->getIsRequired());
        }

        /**
         * @return bool
         * @since 100.2.0
         */
        protected function isTelephoneRequired()
        {
            return ($this->_eavConfig->getAttribute('customer_address', 'telephone')->getIsRequired());
        }

        /**
         * @return bool
         * @since 100.2.0
         */
        protected function isFaxRequired()
        {
            return ($this->_eavConfig->getAttribute('customer_address', 'fax')->getIsRequired());
        }
    }

But it throws Please check the shipping information error. How do I overcome this error? If any modification in my code? If anyone knows please explain me.