So the goal of my itemHandler is to only accept items which already exist in the slot and nothing else. When I try and place lets say yellow wool into a slot that has yellow wool it crashes.

 

Item Handler: https://github.com/BeardlessBrady/Currency-Mod/blob/master-1.10.2/src/main/java/gunn/modcurrency/mod/container/itemhandler/ItemHandlerVendor.java#L26-L38

Crash: https://pastebin.com/jVKYtEW8

This method:

https://github.com/BeardlessBrady/Currency-Mod/blob/master-1.10.2/src/main/java/gunn/modcurrency/mod/container/itemhandler/ItemHandlerVendor.java#L26

is marked non-null. The stack parameter is marked non-null, but yet you check to see if it's null anyway (and if it is, you return it).

ItemStacks can be null in 1.10.2 and earlier, so your ItemStackHandler#insertItem override should be annotated with @Nullable, not @Nonnull. This also applies to the ItemStack parameter.

 

It's only in 1.11 and later that ItemStacks can't be null.

 

This particular crash is triggered by IDEA's automatic runtime null-checking. For methods that you control, fix the annotations or the code so that @Nonnull methods don't return null values. For methods that you don't control, you can disable the null-checking as described here.

Edited July 4, 20178 yr by Choonster

Thank you, I'm backporting to 1.10 from 1.11. At this point I was just trying random things (hence the weird null check)