RuntimeException When i Load Helper Class magento 2

Question

Error When i load my Helper Class Magento2. it shows

1 exception(s): Exception #0 (Magento\Framework\Exception\RuntimeException): Type Error occurred when creating object: Wac\DropPin\Helper\Data

app/code/Wac/DropPin/view/frontend/templates/cart/item/default.phtml

 echo $this->helper('Wac\DropPin\Helper\Data')->productWeight('Test');

app/code/Wac/DropPin/Helper/Data.php

<?php
namespace Wac\DropPin\Helper;

class Data extends \Magento\Framework\App\Helper\AbstractHelper
{
        protected $_productRepository;

    public function __construct(
        \Magento\Backend\Block\Template\Context $context,       
        \Magento\Catalog\Model\ProductRepository $productRepository,
        array $data = []
    )
    {
        $this->_productRepository = $productRepository;
        parent::__construct($context, $data);
    }



    public function productWeight($id)
    {
        return $id;
    }

}

Answer 1

What about this

namespace Wac\DropPin\Helper;

use Magento\Framework\App\Helper\AbstractHelper;

class Data extends AbstractHelper
{

    /**
     * @param \Magento\Framework\App\Helper\Context $context
     */
    public function __construct(
        \Magento\Framework\App\Helper\Context $context
    ) {
        parent::__construct($context);
    }

    // custom method
}

Remember to di compile