A listener class has a series of handlers, each with a `match` and a `handle` closure. Each closure has an optional `origin` parameter.

handler.groovy

handlers.findAll { name, handler ->
    if (handler.match.maximumNumberOfParameters == 1) {
        handler.match notification
    } else {
        handler.match notification, origin
    }
}.each { name, handler ->
    if (handler.handle.maximumNumberOfParameters == 1) {
        handler.handle notification
    } else {
        handler.handle notification, origin
    }
}