Bug in error handling in Shopify::Rest::Base#save

Issue summary

Since v13.0.0 ShopifyAPI::DiscountCode#errors signature has been changed to Hash, and #errors is initialized as Hash nil for DiscountCode resources.

This causes exception in error handling in ShopifyAPI::Rest::Base#save if ShopifyAPI::Errors::HttpResponseError is raised during save operation for DiscountCode resource. Exception is raised because Hash nil does not implement #errors

• shopify_api version: 13.1.0
• Ruby version: 2.7.7

Expected behavior

Rescuing from ShopifyAPI::Errors::HttpResponseError does not raise exception

Actual behavior

#<NoMethodError: undefined method `errors' for {}:Hash> is raised

#<NoMethodError: undefined method `errors' for nil:NilClass> is raised

Edit: corrected details