Fix missing CraftMetaBook#toBuilder override

Spigot-API-Patches/Adventure.patch

@@ -2901,6 +2901,18 @@ diff --git a/src/main/java/org/bukkit/inventory/meta/BookMeta.java b/src/main/ja
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/org/bukkit/inventory/meta/BookMeta.java
 +++ b/src/main/java/org/bukkit/inventory/meta/BookMeta.java
+@@ -0,0 +0,0 @@
+ package org.bukkit.inventory.meta;
+ 
+ import java.util.List;
++
++import net.kyori.adventure.inventory.Book;
+ import net.md_5.bungee.api.chat.BaseComponent;
+ import org.bukkit.Material;
++import org.checkerframework.checker.nullness.qual.NonNull;
+ import org.jetbrains.annotations.NotNull;
+ import org.jetbrains.annotations.Nullable;
+ 
 @@ -0,0 +0,0 @@ import org.jetbrains.annotations.Nullable;
   * Represents a book ({@link Material#WRITABLE_BOOK} or {@link
   * Material#WRITTEN_BOOK}) that can have a title, an author, and pages.
@@ -3017,6 +3029,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        @Override
 +        BookMeta build();
 +    }
++
++    @Override
++    @NonNull
++    BookMetaBuilder toBuilder();
++
 +    // Paper end
 +
      /**

Spigot-Server-Patches/Adventure.patch

@@ -2651,6 +2651,14 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
+@@ -0,0 +0,0 @@ import org.bukkit.craftbukkit.util.CraftChatMessage;
+ import org.bukkit.craftbukkit.util.CraftMagicNumbers;
+ import org.bukkit.inventory.meta.BookMeta;
+ import org.bukkit.inventory.meta.BookMeta.Generation;
++import org.checkerframework.checker.nullness.qual.NonNull;
+ 
+ // Spigot start
+ import static org.spigotmc.ValidateUtils.*;
 @@ -0,0 +0,0 @@ public class CraftMetaBook extends CraftMetaItem implements BookMeta {
          this.generation = (generation == null) ? null : generation.ordinal();
      }
@@ -2783,6 +2791,12 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +            return new CraftMetaBook(title, author, pages);
 +        }
 +    }
++
++    @Override
++    public BookMetaBuilder toBuilder() {
++        return new CraftMetaBookBuilder();
++    }
++
 +    // Paper end
      @Override
      public String getPage(final int page) {