Support for "if" option for "attribute" without a block?

[kapso]

I can do this using attributes -> attributes :slug, if: ->(record) { record.countable? }

...but when I do this using attribute -> attribute :slug, if: ->(record) { record.countable? }

I get the following error - raise ArgumentError, 'No block given in attribute method' unless block

[okuramasafumi]

That's because attribute MUST take a block.
https://github.com/okuramasafumi/alba#simple-serialization-with-root-key