Spree - Skip / exclude a model's attribute validation

product_decorator.rb

Spree::Product.class_eval do
...
  _validators.reject!{ |key, value| key == :shipping_category }
  _validate_callbacks.each do |callback|
    callback.raw_filter.attributes.reject! { |key| key == :shipping_category } if callback.raw_filter.respond_to?(:attributes)
  end
...
end