By some wild reason `pluck` support automatic conversion of serialized attributes: https://github.com/rails/rails/blob/master/activerecord/test/cases/calculations_test.rb#L502

Previously it was held inside `initialize_attributes` but I can not call it directly. I tried to extract required method from https://github.com/rails/rails/blob/master/activerecord/lib/active_record/attribute_methods/serialization.rb#L110 but no shared method was looking better.