def get_receipt(num)
      index = RLP.encode num
      receipt = @receipts[index]

      if receipt == Trie::BLANK_NODE
        raise IndexError, "Receipt does not exist"
      else
        RLP.decode receipt, sedes: Receipt
      end
    end
def get_receipt(num)
      index = RLP.encode num
      receipt = @receipts[index]

      if receipt == Trie::BLANK_NODE
        raise IndexError, "Receipt does not exist"
      else
        RLP.decode receipt, sedes: Receipt
      end
    end
Get the receipt of the `num`th transaction.

 @raise [IndexError] if receipt at index is not found

 @return [Receipt]