Run command from another command

Hi guys
I need help, im make a plugin for my server like this:
Player write in chat /test and this command give diamond to player and run command like /give or /say.
But im have a problem, this is the code:

PHP:

            case "eq1e":
              if($sender->getInventory()->contains(Item::get(10, 0, 1))){
                 $sender->getInventory()->removeItem(Item::get(10, 0, 1));
                 $player = $this->getServer()->getPlayer();
                 $this->getServer()->dispatchCommand($player,"say hello");
               $sender->sendMessage("§aWitaj dziekuje za lave.");
               $sender->sendMessage("§aOd teraz masz nieskonczony zapas mieczy.");
               $sender->sendMessage("§aMozesz je odbierac w magazynie.");
    }
    else{
       $sender->sendMessage("Nie masz lavy!");
    }
               return true;

And when i run the command, it display me " Unknow command"

probably say command doesn't exist

If there is a way to do it directly, don't do it indirectly by running command as a player.

PHP:

pocketmine\command\ConsoleCommandSender; 

https://github.com/PocketMine/Pocke...c/pocketmine/command/ConsoleCommandSender.php

Ummm, what's the point by doin' $this->getServer()->getPlayer() without any argument inside?
https://github.com/PocketMine/PocketMine-MP/blob/master/src/pocketmine/Server.php#L827