Metadata "callback"

Callbacks provides a solution to catch error, status information or data relative to its associated handler. The first two arguments are always the same. The first one is the error object if any. The second is a boolean value representing the status. Status is fundamental to idempotence and indicates if a handler had any impact. The remaining arguments are the one passed from the handler if it was executed asynchronously.

}, function(err, {status}){