The Magento 2 REST API forbids the «null» value for an entity's custom attribute in a «PUT» request

Issues
1

Magento\Framework\Webapi\ServiceInputProcessor::processCustomAttribute()

https://github.com/magento/magento2/blob/2.1.7/lib/internal/Magento/Framework/Webapi/ServiceInputProcessor.php#L259-L267

https://github.com/mage2pro/core/issues/12