def get_transaction(num)
      index = RLP.encode num
      tx = @transactions.get index

      raise IndexError, "Transaction does not exist" if tx == Trie::BLANK_NODE
      RLP.decode tx, sedes: Transaction
    end
def get_transaction(num)
      index = RLP.encode num
      tx = @transactions.get index

      raise IndexError, "Transaction does not exist" if tx == Trie::BLANK_NODE
      RLP.decode tx, sedes: Transaction
    end
Get the `num`th transaction in this block.

 @raise [IndexError] if the transaction does not exist