As propriedades do produto (WC_Abstract_Legacy_Product) não podem ser acessadas diretamente. A correção visa elimitar warnings no error_log, quando apache e versão do WooCommerce >= 3.0

class-wc-intelipost-product-quote.php

<?php

class WC_Intelipost_Quote_Product
{
	private $_packages = array ();
	protected $_simpleProducts = array ();
	private $_dimensions;
	protected $_productsQty = array();

	public function fetchProductQuote($items, $dimensions)
	{
		$this->_dimensions = $dimensions;

		$j = 0;
		foreach ($items as $item_id => $values) 
		{
		    /** @var WC_Product $product */
			$product = $values['data'];
			$qty     = $values['quantity'];

			    $productWidth  = $product->get_width() ? $product->get_width() : $this->_dimensions->_widthAttribute;
	        $productHeight = $product->get_weight() ? $product->get_weight(): $this->_dimensions->_heightAttribute;
	        $productLength = $product->get_length() ? $product->get_length() : $this->_dimensions->_lengthAttribute;
	        $productPrice  = $product->get_price();
	        $productWeight = $this->_dimensions->_getCustomWeight($product->get_weight());
          $productVolume = null;
          //$productVolume = $this->_getVolume ($product);
	        $productSku    = $product->get_sku();
	        $productTitle  = $product->get_title();

	        //$cubic = $this->_getCubic ($productVolume);

	        $data = array( 'packageData' => array(
	                    'width'  => $productWidth,
	                    'height' => $productHeight,
	                    'length' => $productLength,
	                    'price'  => str_replace(',', '.', $productPrice),
	                    'weight' => $productWeight,
	                    'volume' => $productVolume,
	                    'sku'    => $productSku,
	                    'title'  => $productTitle,
	                    'qty'    => $qty,                    
	                ));
	        
			$this->_addToPackage ($data['packageData'], $j ++);
		}
	}

	private function _addToPackage ($packageData, $index)
	{
	    $this->_packages[$index] = $packageData;
	}
		
	public function getPackages()
	{
    	return $this->_packages;
	}	
}