A breaking change had to happen on [email protected] in order to fix both #37 and #64. The reason is explained on this comment.
Basically, for createNumberMask, if the allowEmpty message is set to true, the empty value at version 2.x.x will be null instead of undefined (or empty string). If you never used createNumberMask's allowEmpty option, you should be fine to migrate, otherwise you'll need to test if there's anything broken.