Allow `null` in Product::setCost()
PHP type hinting prevents anything other than the hinted type from being
passed to a function. This includes null
, and we don't want to require
a product cost always be added when adding a product in Magento. Adding
the default = null
to the parameter allows null
to be passed to the
function.
Please review: @ahoffmann @weizhong-wang @lloyd-carter