The JavaDocs show a StonecutterInventory, but it seems to be incompletely implemented.

• Bukkit.createInventory(null, InventoryType.STONECUTTER) does not return StonecutterInventory
• when the player closes the inventory view, the InventoryCloseEvent does not receive a StonecutterInventory.
  • the inventory does show the block the player placed in the inventory, but does not show the result block or the recipe.

Please change Bukkit.createInventory(null, InventoryType.STONECUTTER) to return StoneCutterInventory.

Please extend StoneCutterInventory to provide the result and the recipe chosen.