make inventoryManager.getItem return nil instead of empty table

Author: zyxkad

src/main/java/de/srendi/advancedperipherals/common/addons/computercraft/peripheral/InventoryManagerPeripheral.java

@@ -23,8 +23,8 @@
 import net.minecraftforge.items.wrapper.PlayerArmorInvWrapper;
 import net.minecraftforge.items.wrapper.PlayerInvWrapper;
 import net.minecraftforge.items.wrapper.PlayerOffhandInvWrapper;
-import org.jetbrains.annotations.NotNull;
 
+import org.jetbrains.annotations.NotNull;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
@@ -187,6 +187,11 @@ public final int getFreeSlot() throws LuaException {
         return getOwnerPlayer().getInventory().getFreeSlot();
     }
 
+    @LuaFunction(mainThread = true)
+    public final int getHandSlot() throws LuaException {
+        return getOwnerPlayer().getInventory().selected;
+    }
+
     @LuaFunction(mainThread = true)
     public final Map<String, Object> getItemInHand() throws LuaException {
         return LuaConverter.stackToObjectWithSlot(getOwnerPlayer().getMainHandItem(), getOwnerPlayer().getInventory().selected);

src/main/java/de/srendi/advancedperipherals/common/util/LuaConverter.java

@@ -15,8 +15,9 @@
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.block.state.properties.Property;
 import net.minecraftforge.common.IForgeShearable;
-import org.jetbrains.annotations.NotNull;
 
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -100,8 +101,11 @@ public static Object posToObject(BlockPos pos) {
         return map;
     }
 
+    @Nullable
     public static Map<String, Object> stackToObject(@NotNull ItemStack stack) {
-        if (stack.isEmpty()) return new HashMap<>();
+        if (stack.isEmpty()) {
+            return null;
+        }
         Map<String, Object> map = itemToObject(stack.getItem());
         CompoundTag nbt = stack.copy().getOrCreateTag();
         map.put("count", stack.getCount());
@@ -126,8 +130,11 @@ public static Map<String, Object> stackToObject(@NotNull ItemStack itemStack, in
      * @return a Map containing proper item stack details
      * @see InventoryManagerPeripheral#getItems()
      */
+    @Nullable
     public static Map<String, Object> stackToObjectWithSlot(@NotNull ItemStack stack, int slot) {
-        if (stack.isEmpty()) return new HashMap<>();
+        if (stack.isEmpty()) {
+            return null;
+        }
         Map<String, Object> map = stackToObject(stack);
         map.put("slot", slot);
         return map;