Backport to 1.21.1: Patch EmeraldsForVillagerTypeItem to allow modders to make Custom VillagerTypes

patches/net/minecraft/world/entity/npc/VillagerTrades.java.patch

@@ -0,0 +1,21 @@
+--- a/net/minecraft/world/entity/npc/VillagerTrades.java
++++ b/net/minecraft/world/entity/npc/VillagerTrades.java
+@@ -1477,6 +_,7 @@
+         private final int villagerXp;
+
+         public EmeraldsForVillagerTypeItem(int p_35669_, int p_35670_, int p_35671_, Map<VillagerType, Item> p_35672_) {
++            if (false) // Neo: disable this check so that mods can add custom villager types
+             BuiltInRegistries.VILLAGER_TYPE.stream().filter(p_35680_ -> !p_35672_.containsKey(p_35680_)).findAny().ifPresent(p_339515_ -> {
+                 throw new IllegalStateException("Missing trade for villager type: " + BuiltInRegistries.VILLAGER_TYPE.getKey(p_339515_));
+             });
+@@ -1490,7 +_,9 @@
+         @Override
+         public MerchantOffer getOffer(Entity p_219685_, RandomSource p_219686_) {
+             if (p_219685_ instanceof VillagerDataHolder villagerdataholder) {
+-                ItemCost itemcost = new ItemCost(this.trades.get(villagerdataholder.getVillagerData().getType()), this.cost);
++                Item item = this.trades.get(villagerdataholder.getVillagerData().getType());
++                if (item == null) return null;  // Neo: add a check for unknown villager types
++                ItemCost itemcost = new ItemCost(item, this.cost);
+                 return new MerchantOffer(itemcost, new ItemStack(Items.EMERALD), this.maxUses, this.villagerXp, 0.05F);
+             } else {
+                 return null;