latin-language-toolkit/arethusa — pull request #558 by balmas (2014-12-23 02:41:50+00:00)
Title: prevent undefined exception on undo of attach new aT

trying to clean up uncaught exceptions around handling of artificial tokens --- this fixes one that occurred on undo of an attach of a new artificial token to a head. The redrawing of the edge on the undo was throwing an exception when the head.id was undefined.