--- a/net/minecraft/server/Advancement.java
+++ b/net/minecraft/server/Advancement.java
@@ -27,6 +27,7 @@
     private final String[][] requirements;
     private final Set<Advancement> children = Sets.newLinkedHashSet();
     private final IChatBaseComponent chatComponent;
+    public final org.bukkit.advancement.Advancement bukkit = new org.bukkit.craftbukkit.advancement.CraftAdvancement(this); // CraftBukkit
 
     public Advancement(MinecraftKey minecraftkey, @Nullable Advancement advancement, @Nullable AdvancementDisplay advancementdisplay, AdvancementRewards advancementrewards, Map<String, Criterion> map, String[][] astring) {
         this.key = minecraftkey;
@@ -210,7 +211,7 @@
         }
 
         public Advancement b(MinecraftKey minecraftkey) {
-            if (!this.a((minecraftkey1) -> {
+            if (!this.a((Function<MinecraftKey, Advancement>) (minecraftkey1) -> { // CraftBukkit - decompile error
                 return null;
             })) {
                 throw new IllegalStateException("Tried to build incomplete advancement!");
