amberc.js: checks against length instead of undefined
amberc.js: checks against length instead of undefined

matthias-springer/amber-athens,amber-smalltalk/amber,matthias-springer/amber-athens,amber-smalltalk/amber,adrian-castravete/amber,adrian-castravete/amber,amber-smalltalk/amber,adrian-castravete/amber,matthias-springer/amber-athens