This can be simplified to:
/**
* Before generate Xml
*
* @param \Magento\Framework\View\LayoutInterface $subject
* @return void
*/
public function beforeGenerateXml(\Magento\Framework\View\LayoutInterface $subject)
{
if ($this->depersonalizeChecker->checkIfDepersonalize($subject)) {
$this->defaultTaxBillingAddress = $this->customerSession->getDefaultTaxBillingAddress();
$this->defaultTaxShippingAddress = $this->customerSession->getDefaultTaxShippingAddress();
$this->customerTaxClassId = $this->customerSession->getCustomerTaxClassId();
}
}
A trick: a «before» plugin can return nothing if it needs not modify any argument