PaperMC/patches/server/0668-Fix-incosistency-issue-with-empty-map-items-in-CB.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Sun, 1 Aug 2021 09:49:06 +0100
Subject: [PATCH] Fix incosistency issue with empty map items in CB


diff --git a/src/main/java/net/minecraft/world/item/MapItem.java b/src/main/java/net/minecraft/world/item/MapItem.java
index d407cf849a31a7a77fda07aa687ebb254f43d6ab..45a7e01288f780cf8a812d8e0ae12c4fb79d79e1 100644
--- a/src/main/java/net/minecraft/world/item/MapItem.java
+++ b/src/main/java/net/minecraft/world/item/MapItem.java
@@ -71,7 +71,7 @@ public class MapItem extends ComplexItem {
     public static Integer getMapId(ItemStack stack) {
         CompoundTag nbttagcompound = stack.getTag();
 
-        return nbttagcompound != null && nbttagcompound.contains("map", 99) ? nbttagcompound.getInt("map") : -1; // CraftBukkit - make new maps for no tag
+        return nbttagcompound != null && nbttagcompound.contains("map", 99) ? nbttagcompound.getInt("map") : null; // CraftBukkit - make new maps for no tag // Paper - don't return invalid ID
     }
 
     public static int createNewSavedData(Level world, int x, int z, int scale, boolean showIcons, boolean unlimitedTracking, ResourceKey<Level> dimension) {
diff --git a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaMap.java b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaMap.java
index 6f16f12b4cb9b53878416f1cea532548c418f518..e802623e2ef5fb8c423429335ee7dbabc45a1b74 100644
--- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaMap.java
+++ b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaMap.java
@@ -138,6 +138,7 @@ class CraftMetaMap extends CraftMetaItem implements MapMeta {
 
     @Override
     public int getMapId() {
+        Preconditions.checkState(this.hasMapView(), "Item does not have map associated - check hasMapView() first!"); // Paper - more friendly message
         return this.mapId;
     }