SpigotCore_Main/src/de/steamwar/command/CommandNode.java

@@ -135,4 +135,7 @@ class CommandNode {
                 .findFirst().orElse(false);
     }
 
+    public List<String> suggest(CommandSender commandSender, int index, String[] args, List<Object> mappedObjects) {
+        return null;
+    }
 }