Don't require author and title to be set on signed book meta (#11068)

patches/server/General-ItemMeta-fixes.patch

@@ -457,6 +457,26 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      static final int MAX_PAGE_LENGTH = WritableBookContent.PAGE_EDIT_LENGTH; // SPIGOT-6911: Use Minecraft limits
  
      // We store the pages in their raw original text representation. See SPIGOT-5063, SPIGOT-5350, SPIGOT-3206
+diff --git a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBookSigned.java b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBookSigned.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBookSigned.java
++++ b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBookSigned.java
+@@ -0,0 +0,0 @@ public class CraftMetaBookSigned extends CraftMetaItem implements BookMeta {
+     void applyToItem(CraftMetaItem.Applicator itemData) {
+         super.applyToItem(itemData);
+ 
++        List<Filterable<Component>> list = new ArrayList<>(); // Paper - General ItemMeta Fixes
+         if (this.pages != null) {
+-            List<Filterable<Component>> list = new ArrayList<>();
+             for (Component page : this.pages) {
+                 list.add(Filterable.passThrough(page));
+             }
+-            itemData.put(CraftMetaBookSigned.BOOK_CONTENT, new WrittenBookContent(Filterable.from(FilteredText.passThrough(this.title)), this.author, this.generation, list, this.resolved));
+         }
++        itemData.put(CraftMetaBookSigned.BOOK_CONTENT, new WrittenBookContent(Filterable.from(this.title == null ? FilteredText.EMPTY : FilteredText.passThrough(this.title)), this.author == null ? "" : this.author, this.generation, list, this.resolved)); // Paper - General ItemMeta Fixes
+     }
+ 
+     @Override
 diff --git a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBundle.java b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBundle.java
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaBundle.java