code: private double getLogDiscountFactorForForward(double time) {
  		return discountCurveForForwardRate == null ? -riskFreeRate * time : Math.log(discountCurveForForwardRate.getDiscountFactor(null, time));
  	}
docs: Small helper to calculate rate off the curve or use constant.
  
  @param time Maturity.
  @return The log of the discount factor, i.e., - rate * time.