Ported "stackable empty shulkerboxes on ground" based on @maruohon's tweakeroo code

src/main/java/carpet/helpers/InventoryHelper.java

@@ -0,0 +1,57 @@
+package carpet.helpers;
+
+import net.minecraft.item.ItemStack;
+import net.minecraft.nbt.CompoundTag;
+
+public class InventoryHelper
+{
+    // From nbt/Tag.java createTag()
+    public static final int TAG_END         = 0;
+    public static final int TAG_BYTE        = 1;
+    public static final int TAG_SHORT       = 2;
+    public static final int TAG_INT         = 3;
+    public static final int TAG_LONG        = 4;
+    public static final int TAG_FLOAT       = 5;
+    public static final int TAG_DOUBLE      = 6;
+    public static final int TAG_BYTEARRAY   = 7;
+    public static final int TAG_STRING      = 8;
+    public static final int TAG_LIST        = 9;
+    public static final int TAG_COMPOUND    = 10;
+    public static final int TAG_INTARRAY    = 11;
+    public static final int TAG_LONGARRAY   = 12;
+
+    public static boolean cleanUpShulkerBoxTag(ItemStack stack)
+    {
+        boolean changed = false;
+        CompoundTag tag = stack.getTag();
+
+        if (tag == null || !tag.containsKey("BlockEntityTag", TAG_COMPOUND))
+            return false;
+
+        CompoundTag bet = tag.getCompound("BlockEntityTag");
+        if (bet.containsKey("Items", TAG_LIST) && bet.getList("Items", TAG_COMPOUND).isEmpty())
+        {
+            bet.remove("Items");
+            changed = true;
+        }
+
+        if (bet.isEmpty())
+        {
+            stack.setTag(null);
+            changed = true;
+        }
+
+        return changed;
+    }
+
+    public static boolean shulkerBoxHasItems(ItemStack stack)
+    {
+        CompoundTag tag = stack.getTag();
+
+        if (tag == null || !tag.containsKey("BlockEntityTag", TAG_COMPOUND))
+            return false;
+
+        CompoundTag bet = tag.getCompound("BlockEntityTag");
+        return bet.containsKey("Items", TAG_LIST) && !bet.getList("Items", TAG_COMPOUND).isEmpty();
+    }
+}