http://paste.ee/p/RKpnM

Caused by a lack of a null check here:
https://github.com/austinv11/PeripheralsPlusPlus/blob/master/src/main/java/com/austinv11/peripheralsplusplus/event/PeripheralContainerHandler.java#L21

If a player doesn't have an item equipped, then it will return null.