Replace store with attribute on metadata concern

This change tells active record to always use json as column type in order to work with DBs

Author: JustShah

core/app/models/concerns/spree/metadata.rb

@@ -5,8 +5,8 @@ module Metadata
     extend ActiveSupport::Concern
 
     included do
-      store :customer_metadata, coder: JSON
-      store :admin_metadata, coder: JSON
+      attribute :customer_metadata, :json
+      attribute :admin_metadata, :json
 
       validate :validate_metadata_limits
     end
@@ -21,6 +21,8 @@ def validate_metadata_column(column)
       config = Spree::Config
       metadata = send(column)
 
+      return if metadata.nil?
+
       # Check for maximum number of keys
       validate_metadata_keys_count(metadata, column, config.max_keys)