@type t() :: %ExOanda.TradeOpened{
  client_extensions: ExOanda.ClientExtensions.t() | nil,
  guaranteed_execution_fee: float() | nil,
  half_spread_cost: float() | nil,
  initial_margin_required: float() | nil,
  price: float() | nil,
  quote_guaranteed_execution_fee: float() | nil,
  trade_id: String.t() | nil,
  units: integer() | nil
}