If no atom type is recognized (null is returned), then the ControllerHub.updateAtom() should set the implicit hydrogen count to 0.
fixed in the current JCP pull request: https://github.com/rwst/jchempaint/commit/6c52e4f4c40e630faff6d6d9ca55d8da89264109
fixed in the current JCP pull request:
https://github.com/rwst/jchempaint/commit/6c52e4f4c40e630faff6d6d9ca55d8da89264109