Error in running compile command in magento2

Question

[![<?php
/**
 * Mageplaza_Productslider extension
 *                     NOTICE OF LICENSE
 * 
 *                     This source file is subject to the MIT License
 *                     that is bundled with this package in the file LICENSE.txt.
 *                     It is also available through the world-wide-web at this URL:
 *                     https://www.mageplaza.com/LICENSE.txt
 * 
 *                     @category  Mageplaza
 *                     @package   Mageplaza_Productslider
 *                     @copyright Copyright (c) 2016
 *                     @license   https://www.mageplaza.com/LICENSE.txt
 */
namespace Mageplaza\Productslider\Model\ResourceModel\Slider\Grid;

class Collection extends \Mageplaza\Productslider\Model\ResourceModel\Slider\Collection implements \Magento\Framework\Api\Search\SearchResultInterface
{
    /**
     * Aggregations
     * 
     * @var \Magento\Framework\Search\AggregationInterface
     */
    protected $_aggregations;

    /**
     * constructor
     * 
     * @param \Magento\Framework\Data\Collection\EntityFactoryInterface $entityFactory
     * @param \Psr\Log\LoggerInterface $logger
     * @param \Magento\Framework\Data\Collection\Db\FetchStrategyInterface $fetchStrategy
     * @param \Magento\Framework\Event\ManagerInterface $eventManager
     * @param $mainTable
     * @param $eventPrefix
     * @param $eventObject
     * @param $resourceModel
     * @param $model
     * @param $connection
     * @param \Magento\Framework\Model\ResourceModel\Db\AbstractDb $resource
     */
    public function __construct(
        \Magento\Framework\Data\Collection\EntityFactoryInterface $entityFactory,
        \Psr\Log\LoggerInterface $logger,
        \Magento\Framework\Data\Collection\Db\FetchStrategyInterface $fetchStrategy,
        \Magento\Framework\Event\ManagerInterface $eventManager,
        $mainTable,
        $eventPrefix,
        $eventObject,
        $resourceModel,
        $model = 'Magento\Framework\View\Element\UiComponent\DataProvider\Document',
        $connection = null,
        \Magento\Framework\Model\ResourceModel\Db\AbstractDb $resource = null
    )
    {
        parent::__construct($entityFactory, $logger, $fetchStrategy, $eventManager, $connection, $resource);
        $this->_eventPrefix = $eventPrefix;
        $this->_eventObject = $eventObject;
        $this->_init($model, $resourceModel);
        $this->setMainTable($mainTable);
    }


    /**
     * @return \Magento\Framework\Search\AggregationInterface
     */
    public function getAggregations()
    {
        return $this->_aggregations;
    }

    /**
     * @param \Magento\Framework\Search\AggregationInterface $aggregations
     * @return $this
     */
    public function setAggregations($aggregations)
    {
        $this->_aggregations = $aggregations;
    }


    /**
     * Retrieve all ids for collection
     * Backward compatibility with EAV collection
     *
     * @param int $limit
     * @param int $offset
     * @return array
     */
    public function getAllIds($limit = null, $offset = null)
    {
        return $this->getConnection()->fetchCol($this->_getAllIdsSelect($limit, $offset), $this->_bindParams);
    }

    /**
     * Get search criteria.
     *
     * @return \Magento\Framework\Api\SearchCriteriaInterface|null
     */
    public function getSearchCriteria()
    {
        return null;
    }

    /**
     * Set search criteria.
     *
     * @param \Magento\Framework\Api\SearchCriteriaInterface $searchCriteria
     * @return $this
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function setSearchCriteria(\Magento\Framework\Api\SearchCriteriaInterface $searchCriteria = null)
    {
        return $this;
    }

    /**
     * Get total count.
     *
     * @return int
     */
    public function getTotalCount()
    {
        return $this->getSize();
    }

    /**
     * Set total count.
     *
     * @param int $totalCount
     * @return $this
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function setTotalCount($totalCount)
    {
        return $this;
    }

    /**
     * Set items list.
     *
     * @param \Magento\Framework\Api\ExtensibleDataInterface\[\] $items
     * @return $this
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function setItems(array $items = null)
    {
        return $this;
    }
}]

why i am getting this error ?

can anyone give me idea about it how to fix it immediately ,if i will resolve it i will update this question , thanks

Answer 1

Please use code

\Magento\Framework\DB\Adapter\AdapterInterface  $connection = null,

instead of

$connection = null,

and try compile again.