<type name="MagentoCustomerModelAddressAbstractAddress">
 <plugin name="aroundAddressValidation" type="XxxOptionalLastnamePluginCustomerModelAddressAbstractAddress" sortOrder="10"/>
    </type>

<?php

namespace XxxOptionalLastnamePluginCustomerModelAddress;

class AbstractAddress
{

protected $_directoryData = null;
protected $_eavConfig;

public function __construct(
MagentoDirectoryHelperData $directoryData ,MagentoEavModelConfig $eavConfig
)
{
$this->_directoryData = $directoryData;
$this->_eavConfig = $eavConfig;

}

public function aroundValidate(
MagentoCustomerModelAddressAbstractAddress $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;
} }