It seems like getting an objective from a scoreboard via CraftScoreboard#getScoreboard(String) throws a NullPointerException.

This is probably caused by commit 42ebec1f71b on CraftBukkit. This causes scoreboard related plugins like HealthBar to throw an exception on startup and also leads to other exceptions.

A solution would be to return null when the objective returned by the NMS-Scoreboard is null.

I have added a screenshot of the exception caused by HealthBar while starting the server.