v1.2.5: How to fix Fatal error when viewing order on M2.2.x?

QUESTION:

I upgraded the module to v1.2.5 for my site Magento 2.2.10, when I clicked "view" order, I got error as below:

Fatal error: Uncaught TypeError: Argument 1 passed to Magento\Sales\Model\Order\Invoice::setExtensionAttributes() must implement interface Magento\Sales\Api\Data\InvoiceExtensionInterface, instance of Magento\Sales\Api\Data\OrderExtension given, called in /var/xxxx/xxxx/xxxxx/app/code/Bss/CheckoutCustomField/Model/Observer/Sales/CustomFieldHelper.php on line 94 and defined in /var/xxxxx/xxxxx/xxxx/vendor/magento/module-sales/Model/Order/Invoice.php:1620 Stack trace: #0 /var/xxxx/xxxx/xxxx/app/code/Bss/CheckoutCustomField/Model/Observer/Sales/CustomFieldHelper.php(94): Magento\Sales\Model\Order\Invoice->setExtensionAttributes(Object(Magento\Sales\Api\Data\OrderExtension)) #1 /varxxxx/xxxx/xxxx/app/code/Bss/CheckoutCustomField/Model/Observer/Sales/InvoiceLoadAfter.php(61): Bss\CheckoutCustomField\Model\Observer\Sales\CustomFieldHelper->executeSetExtensionAttributes(Object(Magento\Sales\Model\Order\Interceptor), Object(Magento\Sales\Mod in /var/www/xxxxxx/xxxxxx/xxxxxx/vendor/magento/module-sales/Model/Order/Invoice.php on line 1620

Please tell me how to fix it?

ANSWER:

This error only appears on M2.2.x, to fix this error, please edit file app/code/Bss/CheckoutCustomField/Model/Observer/Sales/CustomFieldHelper.php as below: 

Or download the attached file below and overwrite the current file on your site.

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