diff --git a/src/main/java/net/minestom/server/inventory/TransactionOption.java b/src/main/java/net/minestom/server/inventory/TransactionOption.java
index 313f9a3ed..0fa871d87 100644
--- a/src/main/java/net/minestom/server/inventory/TransactionOption.java
+++ b/src/main/java/net/minestom/server/inventory/TransactionOption.java
@@ -13,7 +13,7 @@ public interface TransactionOption<T> {
      * <p>
      * The remaining, can be air.
      */
-    TransactionOption<@NotNull ItemStack> ALL = (inventory, result, itemChangesMap) -> {
+    TransactionOption<ItemStack> ALL = (inventory, result, itemChangesMap) -> {
         itemChangesMap.forEach(inventory::safeItemInsert);
         return result;
     };
@@ -23,7 +23,7 @@ public interface TransactionOption<T> {
      * <p>
      * Returns true if the item has been added, false if nothing changed.
      */
-    TransactionOption<@NotNull Boolean> ALL_OR_NOTHING = (inventory, result, itemChangesMap) -> {
+    TransactionOption<Boolean> ALL_OR_NOTHING = (inventory, result, itemChangesMap) -> {
         if (result.isAir()) {
             // Item can be fully placed inside the inventory, do so
             itemChangesMap.forEach(inventory::safeItemInsert);
@@ -39,7 +39,7 @@ public interface TransactionOption<T> {
      * <p>
      * Returns true if the item can be fully added, false otherwise.
      */
-    TransactionOption<@NotNull Boolean> DRY_RUN = (inventory, result, itemChangesMap) -> result.isAir();
+    TransactionOption<Boolean> DRY_RUN = (inventory, result, itemChangesMap) -> result.isAir();
 
     @NotNull T fill(@NotNull AbstractInventory inventory,
                     @NotNull ItemStack result,
diff --git a/src/main/java/net/minestom/server/inventory/TransactionType.java b/src/main/java/net/minestom/server/inventory/TransactionType.java
index 80f2fe97d..fa0bafc67 100644
--- a/src/main/java/net/minestom/server/inventory/TransactionType.java
+++ b/src/main/java/net/minestom/server/inventory/TransactionType.java
@@ -12,6 +12,7 @@ import java.util.Map;
 /**
  * Represents a type of transaction that you can apply to an {@link AbstractInventory}.
  */
+@FunctionalInterface
 public interface TransactionType {
 
     /**