I've just upgraded magento version from 1.6 to 1.9.1.1. I go to system/configuration/sales/payment methods and got the following error:

![wrong content type][1]


I have tried to debug by going to this function on app/code/core/Mage/Usa/Model/Shipping/Carrier/Dhl/International.php:

    public function getAllowedMethods()
        {
            $contentType = $this->getConfigData('content_type');
            $allowedMethods = array();
            if ($this->_isDomestic) {
                $allowedMethods = array_merge(explode(',', $this->getConfigData('doc_methods')),
                    explode(',', $this->getConfigData('nondoc_methods'))
                );
            } else {
                switch ($contentType) {
                    case self::DHL_CONTENT_TYPE_DOC:
                        $allowedMethods = explode(',', $this->getConfigData('doc_methods'));
                        break;
                    case self::DHL_CONTENT_TYPE_NON_DOC:
                        $allowedMethods = explode(',', $this->getConfigData('nondoc_methods'));
                        break;
                    default:
                        Mage::throwException(Mage::helper('usa')->__('Wrong Content Type.'));
                }
            }
            $methods = array();
            foreach ($allowedMethods as $method) {
                $methods[$method] = $this->getDhlProductTitle($method);
            }
            return $methods;
        } 

   

I tried to **var_dump($contentType)** add get **NULL** value. What's wrong here ?

**UPDATE:**

My Content Type config in admin panel:

![content type DHL][2]


  [1]: https://i.sstatic.net/Lyyxg.png
  [2]: https://i.sstatic.net/PUrb5.png