According to [this](https://stackoverflow.com/questions/14112515/semicolon-at-end-of-if-statement) it would compile, but it does nothing (except for "wasting" a few cycles). Didn't really bother testing myself. The whole thing can be simplified down to:
```
return !(slotIndex == OUTPUT_LEFT_INVENTORY_INDEX || slotIndex == OUTPUT_RIGHT_INVENTORY_INDEX || slotIndex == FUEL_INVENTORY_INDEX);
```
or this one (whichever is preferred):
```
return slotIndex != OUTPUT_LEFT_INVENTORY_INDEX && slotIndex != OUTPUT_RIGHT_INVENTORY_INDEX && slotIndex != FUEL_INVENTORY_INDEX;
```