Как объединить две колонки в сетке в админ панели magento 2

Question

Мне нужно объединить два столбца в сетке моей панели администратора. Это мой код.

<?php

namespace Bridge\Tradeuser\Block\Adminhtml\Customer\Grid;
use Magento\Customer\Controller\RegistryConstants; 
class Owners extends \Magento\Backend\Block\Widget\Grid\Extended {

    protected $_coreRegistry = null;
    protected $collectionFactory;
    protected $_customerFactory;
    protected $_objectManager;

    public function __construct(
    \Magento\Backend\Block\Template\Context $context,
    \Magento\Backend\Helper\Data $backendHelper,
    \Magento\Framework\View\Element\UiComponent\DataProvider\CollectionFactory $collectionFactory,
    \Magento\Framework\Registry $coreRegistry,
    \Magento\Customer\Model\CustomerFactory $customerFactory,
    \Magento\Framework\ObjectManagerInterface $objectManager,
    array $data = []
    ) {
        $this->_coreRegistry      = $coreRegistry;
        $this->_collectionFactory = $collectionFactory;
        $this->_customerFactory   = $customerFactory;
        $this->_objectManager     = $objectManager; 
        parent::__construct($context, $backendHelper, $data);
    }

    protected function _construct() {
        parent::_construct();
        $this->setId('id');
        $this->setDefaultSort('id', 'desc');
        $this->setUseAjax(true);
    }

    protected function _prepareCollection() {

        $customer   = $this->_customerFactory->create();
        $customer   = $customer->load($this->_coreRegistry->registry(RegistryConstants::CURRENT_CUSTOMER_ID))->getData();
        $collection = $this->_objectManager->create('Bridge\Tradeuser\Model\Tradeuser')->getCollection()->addFieldToFilter(
                'customer_id', $customer['entity_id']
        );
        $this->setCollection($collection);         
        return parent::_prepareCollection();
    }

    protected function _prepareColumns() {

        $this->addColumn('id', ['header' => __('Owners'), 'width' => '100', 'index' => 'id']);        
        $this->addColumn('owner_first_name', ['header' => __('Owner First Name'), 'width' => '100', 'index' => 'owner_first_name', 'type' => 'text']);
        $this->addColumn('owner_last_name', ['header' => __('Owner Last Name'), 'width' => '100', 'index' => 'owner_last_name', 'type' => 'text']);
        $this->addColumn('owner_email', ['header' => __('Owner Email'), 'width' => '100', 'index' => 'owner_email', 'type' => 'text']);
        $this->addColumn('owner_address', ['header' => __('Owner Address'), 'width' => '100', 'index' => 'owner_address', 'type' => 'text']);
        $this->addColumn('owner_postcode', ['header' => __('Owner postcode'), 'width' => '100', 'index' => 'owner_postcode', 'type' => 'text']);
        $this->addColumn('owner_phone', ['header' => __('Owner Phone'), 'width' => '100', 'index' => 'owner_phone', 'type' => 'text']);
        $this->addColumn('owner_fax', ['header' => __('Owner Fax'), 'width' => '100', 'index' => 'owner_fax', 'type' => 'text']);
        $this->addColumn('created_at', ['header' => __('Create Date'), 'width' => '100', 'index' => 'created_at', 'type' => 'date']);         
        return parent::_prepareColumns();
    } 
}

Мне нужно объединить owner_first_name и owner_last_name в owner_name. Я попытался следующий код, но он выдает ошибку, как A technical problem with the server created an error. Try again to continue what you were doing. If the problem persists, try again later.

$this->addColumn('owner_first_name', 
    array(
        'header'       => $this->__('Owner Name'),
        'sortable'     => true,
        'index'        => array('owner_first_name', 'owner_last_name'),
        'type'         => 'concat',
        'separator'    => '  ',
        'filter_index' => "CONCAT(owner_first_name, '  ', owner_last_name)",
        'width'        => '140px',
    )
);