Fix optional argument registration error

+ fixed exception appearing in server log, this isn't done with VarHandles but I think because this is a hotfix, it is fine for now.
I will handle all this properly on dev/commandapi-paper and CommandAPI#517

Author: DerEchtePilz

commandapi-platforms/commandapi-bukkit/commandapi-bukkit-nms/commandapi-bukkit-1.20.5/src/main/java/dev/jorel/commandapi/nms/NMS_1_20_R4.java

@@ -210,6 +210,7 @@ public class NMS_1_20_R4 extends NMS_Common {
 	private static final Field entitySelectorUsesSelector;
 	// private static final SafeVarHandle<ItemInput, CompoundTag> itemInput;
 	private static final Field serverFunctionLibraryDispatcher;
+	private static final Field vanillaCommandDispatcher;
 
 	// Derived from net.minecraft.commands.Commands;
 	private static final CommandBuildContext COMMAND_BUILD_CONTEXT;
@@ -230,6 +231,13 @@ public class NMS_1_20_R4 extends NMS_Common {
 		// itemInput = SafeVarHandle.ofOrNull(ItemInput.class, "c", "tag", CompoundTag.class);
 		// For some reason, MethodHandles fails for this field, but Field works okay
 		serverFunctionLibraryDispatcher = CommandAPIHandler.getField(ServerFunctionLibrary.class, "g", "dispatcher");
+		Field commandDispatcher;
+		try {
+			commandDispatcher = MinecraftServer.class.getDeclaredField("vanillaCommandDispatcher");
+		} catch (NoSuchFieldException | SecurityException e) {
+			commandDispatcher = null;
+		}
+		vanillaCommandDispatcher = commandDispatcher;
 	}
 
 	private static NamespacedKey fromResourceLocation(ResourceLocation key) {
@@ -895,7 +903,11 @@ public final boolean isVanillaCommandWrapper(Command command) {
 
 	@Override
 	public Command wrapToVanillaCommandWrapper(CommandNode<CommandSourceStack> node) {
-		return new VanillaCommandWrapper(this.<MinecraftServer>getMinecraftServer().vanillaCommandDispatcher, node);
+		if (vanillaCommandDispatcher != null) {
+			return new VanillaCommandWrapper(this.<MinecraftServer>getMinecraftServer().vanillaCommandDispatcher, node);
+		} else {
+			return new VanillaCommandWrapper(this.<MinecraftServer>getMinecraftServer().getCommands(), node);
+		}
 	}
 
 	@Override

commandapi-platforms/commandapi-bukkit/commandapi-bukkit-nms/commandapi-bukkit-nms-common/src/main/java/dev/jorel/commandapi/nms/NMS_Common.java

@@ -70,6 +70,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.lang.reflect.Field;
 import java.util.*;
 import java.util.function.Function;
 import java.util.function.Predicate;
@@ -93,10 +94,16 @@
  */
 public abstract class NMS_Common extends CommandAPIBukkit<CommandSourceStack> {
 
-	private static final SafeVarHandle<MinecraftServer, CommandDispatcher> commandDispatcher;
+	private static final Field commandDispatcher;
 
 	static {
-		commandDispatcher = SafeVarHandle.ofOrNull(MinecraftServer.class, "vanillaCommandDispatcher", "vanillaCommandDispatcher", CommandDispatcher.class);
+		Field temporary;
+		try {
+			temporary = MinecraftServer.class.getDeclaredField("vanillaCommandDispatcher");
+		} catch (Exception e) {
+			temporary = null;
+		}
+		commandDispatcher = temporary;
 	}
 
 	private static NamespacedKey fromResourceLocation(ResourceLocation key) {