WinForm "read and validate" a string :    Hi im a newe on c# i get the error that "not all code paths return a value" appreciate the help why, or how i should write it.  


      private string ReadDescription(out bool success)
        {
            success = false;
            if (txtDescription.Text == "")
            {
                GiveMessage("Ivalid description");
                success = false;
            }
            else
                success = true;  

//here is were the method is going.

     private ShoppingItem ReadInput(out bool success)
        {
            success = false;
            ShoppingItem item = new ShoppingItem();
            item.Descritption = ReadDescription(out success); //<----
            if (!success)
                return null;
            item.Amount = ReadAmount(out success);
            if (!success)
                return null;
            item.Unit = ReaUnit(out success);
            if (!success)
                return item;
        }

