Index Type with composite key

[chripalombella]

Hi,
i have to index a type with a composite key:

    Site site
    User user


    static constraints = {
    }

    static belongsTo = [Site, User]


    static mapping = {
        id composite: ["user", "site"]
    }

    static searchable = {
        site component : true
        user component : true
    }

But when i save, i got this error:

ERROR grails.plugins.elasticsearch.index.IndexRequestQueue - Error Indexing class ---classname--- (index: ---indexname--- , type: ---tipename---) of id null