diff --git a/src/main/java/de/iani/treasurechest/database/TreasureChestDatabase.java b/src/main/java/de/iani/treasurechest/database/TreasureChestDatabase.java
index 9e82f9e..b83e7c9 100644
--- a/src/main/java/de/iani/treasurechest/database/TreasureChestDatabase.java
+++ b/src/main/java/de/iani/treasurechest/database/TreasureChestDatabase.java
@@ -74,13 +74,13 @@
             long time = System.currentTimeMillis();
             smt.setLong(2, time);
             YamlConfiguration conf = new YamlConfiguration();
-            conf.set("display", item.getDisplayItem());
+            conf.set("display", item.getDisplayItem() == null ? null : item.getDisplayItem().serializeAsBytes());
             ConfigurationSection itemsSection = conf.createSection("items");
             ItemStack[] items = item.getPriceItems();
             if (items != null) {
                 for (int i = 0; i < items.length; i++) {
                     ItemStack stack = items[i];
-                    itemsSection.set(Integer.toString(i), stack);
+                    itemsSection.set(Integer.toString(i), stack == null ? null : stack.serializeAsBytes());
                 }
             }
             conf.set("money", item.getPriceMoney());
@@ -104,13 +104,13 @@
             PreparedStatement smt = sqlConnection.getOrCreateStatement(updateContent);
 
             YamlConfiguration conf = new YamlConfiguration();
-            conf.set("display", item.getDisplayItem());
+            conf.set("display", item.getDisplayItem() == null ? null : item.getDisplayItem().serializeAsBytes());
             ConfigurationSection itemsSection = conf.createSection("items");
             ItemStack[] items = item.getPriceItems();
             if (items != null) {
                 for (int i = 0; i < items.length; i++) {
                     ItemStack stack = items[i];
-                    itemsSection.set(Integer.toString(i), stack);
+                    itemsSection.set(Integer.toString(i), stack == null ? null : stack.serializeAsBytes());
                 }
             }
             conf.set("money", item.getPriceMoney());
@@ -138,7 +138,7 @@
                     plugin.getLogger().log(Level.WARNING, "Could not load treasure chest item " + id + " for player " + owner, e);
                     continue;
                 }
-                ItemStack displayItem = conf.getItemStack("display");
+                ItemStack displayItem = getStack(conf, "display");
                 if (displayItem == null || displayItem.getAmount() == 0 || displayItem.getType() == Material.AIR) {
                     plugin.getLogger().log(Level.WARNING, "No display item for item " + id + " for player " + owner);
                     continue;
@@ -146,7 +146,7 @@
                 ArrayList<ItemStack> stacks = new ArrayList<>();
                 ConfigurationSection itemsSection = conf.getConfigurationSection("items");
                 for (String key : itemsSection.getKeys(false)) {
-                    ItemStack stack = itemsSection.getItemStack(key);
+                    ItemStack stack = getStack(itemsSection, key);
                     if (stack != null && stack.getAmount() > 0 && stack.getType() != Material.AIR) {
                         stacks.add(stack);
                     }
@@ -160,6 +160,11 @@
         });
     }
 
+    private ItemStack getStack(ConfigurationSection conf, String key) {
+        Object object = conf.get(key);
+        return object instanceof ItemStack stack ? stack : object instanceof byte[] bytes ? ItemStack.deserializeBytes(bytes) : null;
+    }
+
     public ArrayList<DatabaseTreasureChestItem> getAllItems() throws SQLException {
         return this.connection.runCommands((connection, sqlConnection) -> {
             ArrayList<DatabaseTreasureChestItem> result = new ArrayList<>();
@@ -176,7 +181,7 @@
                     plugin.getLogger().log(Level.WARNING, "Could not load treasure chest item " + id, e);
                     continue;
                 }
-                ItemStack displayItem = conf.getItemStack("display");
+                ItemStack displayItem = getStack(conf, "display");
                 if (displayItem == null || displayItem.getAmount() == 0 || displayItem.getType() == Material.AIR) {
                     plugin.getLogger().log(Level.WARNING, "No display item for item " + id);
                     continue;
@@ -184,7 +189,7 @@
                 ArrayList<ItemStack> stacks = new ArrayList<>();
                 ConfigurationSection itemsSection = conf.getConfigurationSection("items");
                 for (String key : itemsSection.getKeys(false)) {
-                    ItemStack stack = itemsSection.getItemStack(key);
+                    ItemStack stack = getStack(itemsSection, key);
                     if (stack != null && stack.getAmount() > 0 && stack.getType() != Material.AIR) {
                         stacks.add(stack);
                     }