lib/async.js
function done(result, callback) {
  if (!_.isFunction(callback)) return
  process.nextTick(function () { callback(null, result) })
}
function done(result, callback) {
  if (!_.isFunction(callback)) return
  process.nextTick(function () { callback(null, result) })
}
function done ( result , callback ) { if ( ! _ . isFunction ( callback ) ) return process . nextTick ( function ( ) { callback ( null , result ) } ) }
wrap async success callback
wrap async success callback