Fixed sendmessage command output.

Also clarified coop command in help command.

src/main/java/emu/grasscutter/command/commands/SendMessageCommand.java

@@ -15,7 +15,7 @@ public final class SendMessageCommand implements CommandHandler {
     @Override
     public void execute(Player sender, Player targetPlayer, List<String> args) {
         if (args.size() == 0) {
-            CommandHandler.sendMessage(null, translate(sender, "commands.sendMessage.usage"));
+            CommandHandler.sendMessage(sender, translate(sender, "commands.sendMessage.usage"));
             return;
         }
 

src/main/resources/languages/en-US.json

@@ -136,7 +136,7 @@
     "coop": {
       "usage": "Usage: coop [host UID]",
       "success": "Summoned %s to %s's world.",
-      "description": "Forces someone to join the world of others"
+      "description": "Forces someone to join the world of others. If no one is targeted, it sends you into co-op mode anyway."
     },
     "enter_dungeon": {
       "usage": "Usage: enterdungeon <dungeonID>",