heres a guide for you, im pretty sure u can do it on ur own :)
http://www.maxcheaters.com/forum/index.php?topic=50068.0
Try to understand how l2j works and ull be doing amazing stuff in a short period of time :P
what pack are you using?
This may be a shitty code in the doPickup AIAccessor.
Or the doPickUp itself method :/
Is the project live?
Cus if it is:
U'll need to read the rules again :/
thats a null pointer :P not a array exception.
Anyway make sure the packet that ist being cloned is not null, archid's dummy packets are set as null :P