def finalize
      @transactions.sort! { |a, b| a.date <=> b.date }
      balance = Value.new(0)
      @balances = @transactions.map do |act_txn|
        balance += act_txn.value
        {
          date: act_txn.date,
          value: balance,
        }
      end
    end
def finalize
      @transactions.sort! { |a, b| a.date <=> b.date }
      balance = Value.new(0)
      @balances = @transactions.map do |act_txn|
        balance += act_txn.value
        {
          date: act_txn.date,
          value: balance,
        }
      end
    end
Internal method used to complete initialization of the Account after
 all transactions have been associated with it.

 @return [void]