Reproduce for sveltekit transport did not encode falsy value

Despite the docs says that encode should return false for anything that isn’t an instance of the type, returning falsy value, including 0, will not encode the type.

Each transporter contains an encode function, which encodes values on the server (or returns false for anything that isn’t an instance of the type) and a corresponding decode function

We have a custom Role class (src/lib/role.js). We have define transport hooks (src/hooks.js), where it just return number representation of Role. However, if the number is 0, sveltekit throws cannot stringify arbitrary non-POJOs.

Error: Data returned from `load` while rendering / is not serializable: Cannot
stringify arbitrary non-POJOs (data.role)

Running

npm run dev