Currently there exists no Composter InventoryType.
This becomes an issue when using code to filter out non-chest InventoryMoveItemEvents.
The below code works fine for chest-related hopper inventory siphoning.
However if the Hopper-Composter-Hopper auto-composter shown in the supplied image is built it will pass the above code's if statement. This is because Composters report a Chest InventoryType.
The above code will also throw an NPE when loc is set, as the getSource().getLocation() is null (probably related to the missing InventoryType somehow.)