if (beginExecutionPeriod == null) { throw new DomainException(""); }
    private void initBeginExecutionPeriodForDegreeCurricularPlan(final CourseGroup courseGroup,	    final ExecutionPeriod beginExecutionPeriod) {	for (final CurricularRule curricularRule : courseGroup.getCurricularRules()) {	    curricularRule.setBegin(beginExecutionPeriod);	}	for (final Context context : courseGroup.getChildContexts()) {	    context.setBeginExecutionPeriod(beginExecutionPeriod);	    if (!context.getChildDegreeModule().isLeaf()) {		initBeginExecutionPeriodForDegreeCurricularPlan((CourseGroup) context			.getChildDegreeModule(), beginExecutionPeriod);	    }	}    }