fix static

Author: engcom-Charlie

app/code/Magento/Dhl/Model/Carrier.php

@@ -1768,9 +1768,8 @@ protected function _shipmentDetails($xml, $rawRequest, $originRegion = '')
          */
         $nodeShipmentDetails->addChild('DoorTo', 'DD');
         $nodeShipmentDetails->addChild('DimensionUnit', substr($this->_getDimensionUnit(), 0, 1));
-        if ($package['params']['container'] == self::DHL_CONTENT_TYPE_NON_DOC) {
-            $packageType = 'CP';
-        }
+        $contentType = isset($package['params']['container']) ? $package['params']['container'] : '';
+        $packageType = $contentType === self::DHL_CONTENT_TYPE_NON_DOC ? 'CP' : '';
         $nodeShipmentDetails->addChild('PackageType', $packageType);
         if ($this->isDutiable($rawRequest->getOrigCountryId(), $rawRequest->getDestCountryId())) {
             $nodeShipmentDetails->addChild('IsDutiable', 'Y');