You can now whitelist items, only these items will be stacked.
A whitelist.yml file is automatically generated. You will be able to stack only itemstack, so the whitelist is complete.
Code (whitelistyml (Unknown Language)):
enableWhitelist: true
whitelist:
'1':
material: MELON
data: 0
amount: 1
durability: 0
'2':
material: CACTUS
data: 0
amount: 1
durability: 0