Send remove_keyboard if empty string is passed; (#2)

Co-authored-by: Ilya Mazlov <mazlov.i.a@gmail.com>

Author: Laxilef

src/UniversalTelegramBot.cpp

@@ -594,8 +594,11 @@ bool UniversalTelegramBot::sendMessageWithReplyKeyboard(
     payload["parse_mode"] = parse_mode;
 
   JsonObject replyMarkup = payload.createNestedObject("reply_markup");
-    
-  replyMarkup["keyboard"] = serialized(keyboard);
+  
+  if (keyboard.isEmpty())
+    replyMarkup["remove_keyboard"] = true;
+  else
+    replyMarkup["keyboard"] = serialized(keyboard);
 
   // Telegram defaults these values to false, so to decrease the size of the
   // payload we will only send them if needed