if (executionPeriod.isAfter(firstExecutionPeriod)) {
if (executionPeriod != null && executionPeriod.isAfter(firstExecutionPeriod)) {
    public double getBalanceOfCreditsUntil(ExecutionPeriod executionPeriod) throws ParseException {	double balanceCredits = 0.0;	ExecutionPeriod firstExecutionPeriod = TeacherService.getStartExecutionPeriodForCredits();	TeacherService firstTeacherService = getTeacherServiceByExecutionPeriod(firstExecutionPeriod);	if (firstTeacherService != null) {	    balanceCredits = firstTeacherService.getPastServiceCredits();	}	if (executionPeriod.isAfter(firstExecutionPeriod)) {	    balanceCredits = sumCreditsBetweenPeriods(firstExecutionPeriod.getNextExecutionPeriod(),		    executionPeriod, balanceCredits);	}	return balanceCredits;    }