PaperMC/paper-server/patches/sources/net/minecraft/server/commands/DifficultyCommand.java.patch

--- a/net/minecraft/server/commands/DifficultyCommand.java
+++ b/net/minecraft/server/commands/DifficultyCommand.java
@@ -44,11 +44,12 @@
 
     public static int setDifficulty(CommandSourceStack source, Difficulty difficulty) throws CommandSyntaxException {
         MinecraftServer minecraftserver = source.getServer();
+        net.minecraft.server.level.ServerLevel worldServer = source.getLevel(); // CraftBukkit
 
-        if (minecraftserver.getWorldData().getDifficulty() == difficulty) {
+        if (worldServer.getDifficulty() == difficulty) { // CraftBukkit
             throw DifficultyCommand.ERROR_ALREADY_DIFFICULT.create(difficulty.getKey());
         } else {
-            minecraftserver.setDifficulty(difficulty, true);
+            worldServer.serverLevelData.setDifficulty(difficulty); // CraftBukkit
             source.sendSuccess(() -> {
                 return Component.translatable("commands.difficulty.success", difficulty.getDisplayName());
             }, true);