Fix annotations

src/main/java/com/github/steveice10/mc/protocol/codec/MinecraftCodecHelper.java

@@ -242,7 +242,7 @@ public class MinecraftCodecHelper extends BasePacketCodecHelper {
         return new ItemStack(item, buf.readByte(), this.readAnyTag(buf));
     }
 
-    public void writeItemStack(ByteBuf buf, ItemStack item) throws IOException {
+    public void writeItemStack(ByteBuf buf, @Nullable ItemStack item) throws IOException {
         buf.writeBoolean(item != null);
         if (item != null) {
             this.writeVarInt(buf, item.getId());

src/main/java/com/github/steveice10/mc/protocol/packet/ingame/serverbound/inventory/ServerboundSetCreativeModeSlotPacket.java

@@ -8,6 +8,7 @@ import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.NonNull;
 import lombok.With;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.io.IOException;
 
@@ -16,7 +17,7 @@ import java.io.IOException;
 @AllArgsConstructor
 public class ServerboundSetCreativeModeSlotPacket implements MinecraftPacket {
     private final int slot;
-    private final ItemStack clickedItem;
+    private final @Nullable ItemStack clickedItem;
 
     public ServerboundSetCreativeModeSlotPacket(ByteBuf in, MinecraftCodecHelper helper) throws IOException {
         this.slot = in.readShort();