The method appendInternal in the ToStringStyle Class throw a java.lang.NullPointerException when the value that is given is null.
The exception is thrown in line 414 because there is no null check in the CustomToStringStyle class near line 160 which use the appendInternal method.
I hope i can help with that
Thanks, that was previously found and fixed, see http://sourceforge.net/p/jackcess/discussion/456474/thread/26506951/?limit=25#5173/b9a9/b8bb