This makes sense if you want to get the border property. However when animating the border, when one border (for example the top) is different, it will return null which causes an error here: https://github.com/kamicane/moofx/blob/master/lib/browser.js#L567 (because null doesn't have a replace method).
I think when it's detected that the borders are different, it should change
border: '1px solid red'
borderTop: '1px solid red',
borderRight: '1px solid red',
borderBottom: '1px solid red',
borderLeft: '1px solid red'
so all borders do animate to the desired value, and it would prevent the error.