Looks like another breakEvent changing mod may not have setup fake player in way that TreeChopper expects? Can't really tell what is null. Full dump here: at paste bin. Mod Versions for stuff from the stacktrace:

• TreeChopper-1.12.2-1.2.4.jar
• QuickLeafDecay-MC1.12.1-1.2.4.jar
• NetherEx-1.12-2.1.14.15.jar
• Cyclic-1.12.2-1.11.1.jar
• and Forge 2555 (kindof old this one...)

[18:36:01] [Server thread/ERROR] [FML]: Exception caught during firing event net.minecraftforge.event.world.BlockEvent$BreakEvent@fba2be8:
java.lang.NullPointerException: null
at treechopper.proxy.CommonProxy.DestroyWoodBlock(CommonProxy.java:115) ~[CommonProxy.class:?]
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_210_CommonProxy_DestroyWoodBlock_BreakEvent.invoke(.dynamic) ~[?:?]
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90) ~[ASMEventHandler.class:?]
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:179) [EventBus.class:?]
at net.minecraftforge.common.ForgeHooks.onBlockBreakEvent(ForgeHooks.java:813) [ForgeHooks.class:?]
[SNIP]