Fixed unknown blocks dropping themselves

src/pocketmine/block/UnknownBlock.php

@@ -23,9 +23,15 @@ declare(strict_types=1);
 
 namespace pocketmine\block;
 
+use pocketmine\item\Item;
+
 class UnknownBlock extends Transparent{
 
 	public function getHardness(){
 		return 0;
 	}
+
+	public function getDrops(Item $item){
+		return [];
+	}
 }