andrewdolce/Abacus — comment on commit b06b1c1e8daa0c49df9cbc52048f6404acf0fad3
File: src/abacus.tween.js line 44
By gnarf37:

`preferredIndex != null` might be a better check for `null/undefined`, Even just `preferredIndex !== undefined`

I think `arguments.length` can have wacky repercussions for detecting the number of arguments when the function defines more than are used...