As browsers support prefixless transforms, $(elem).css('transform') will return "none" rather than the empty string. That will cause "$(elem).css('transform') || new Transform();" to not get to the new Transform() bit, obviously.
You probably need to add a clause that compares against "none".
Opera 12.02:
>>> $('.field').css('transform')
""
>>> $('.field').css('-o-transform')
"none"
Chrome:
>>> $('.field').css('transform')
""
>>> $('.field').css('-webkit-transform')
"none"
ie9:
>>> $('.field').css('transform')
""
>>> $('.field').css('-ms-transform')
"none"
Opera Next:
>>> $('.field').css('transform')
"none"
>>> $('.field').css('-o-transform')
"none"
Not sure when Firefox, Chrome, and IE10 hit the streets with their prefixless versions, but they're on their way.