fix: crash on close book

Closes #312

Author: klikli-dev

common/src/main/java/com/klikli_dev/modonomicon/client/gui/BookGuiManager.java

@@ -499,11 +499,12 @@ public void closeParentScreen(BookParentScreen screen) {
     protected void sendBookClosedMessage(BookParentScreen screen) {
         var player = Minecraft.getInstance().player;
         if (player != null) {
-            //If the book in the main hand is this book, we send MAIN_HAND, otherwise OFF_HAND
+            //If there is a book in the main hand and it is the closed screen's book, we send MAIN_HAND, otherwise OFF_HAND
             //That means if the book is in neither hand, we send OFF_HAND
             //that is fine, the server will then just not update the closed state nbt on any item.
             //this is for the case of a custom button opening the book gui while the book is not in hand
-            if (ModonomiconItem.getBook(player.getMainHandItem()).getId().equals(screen.getBook().getId()))
+            var bookInMainhand = ModonomiconItem.getBook(player.getMainHandItem());
+            if (bookInMainhand != null && screen.getBook().getId().equals(bookInMainhand.getId()))
                 Services.NETWORK.sendToServer(new BookClosedMessage(InteractionHand.MAIN_HAND));
             else
                 Services.NETWORK.sendToServer(new BookClosedMessage(InteractionHand.OFF_HAND));

common/src/main/java/com/klikli_dev/modonomicon/networking/BookClosedMessage.java

@@ -5,6 +5,7 @@
 package com.klikli_dev.modonomicon.networking;
 
 import com.klikli_dev.modonomicon.Modonomicon;
+import com.klikli_dev.modonomicon.item.ModonomiconItem;
 import com.klikli_dev.modonomicon.util.StreamCodecs;
 import net.minecraft.network.RegistryFriendlyByteBuf;
 import net.minecraft.network.codec.StreamCodec;
@@ -43,8 +44,8 @@ public void onServerReceived(MinecraftServer server, ServerPlayer player) {
 
         //Only set to closed if it is a modonomicon with a valid book.
         //The item in hand could be anything if the book screen was opened e.g. via a custom UI button.
-        if (com.klikli_dev.modonomicon.item.ModonomiconItem.getBook(stack) != null) {
-            com.klikli_dev.modonomicon.item.ModonomiconItem.setBookClosed(stack);
+        if (ModonomiconItem.getBook(stack) != null) {
+            ModonomiconItem.setBookClosed(stack);
         }
     }
 }