if条件习惯性忘记考虑else情况

long recommendClassId = classId;
List<SchoolClass> schoolClassList = schoolClassMapper.getAvailableClassByTeacherId(classIds, GradeUtils.getGraduateYear(),
                SchoolClassStatus.Normal.getId());
List<SchoolClass> schoolClasses = Lists.newArrayListWithCapacity(schoolClassList.size());
SchoolClass recommendSchoolClass = schoolClassList
                .stream()
                .filter(schoolClass -> schoolClass.getId() == recommendClassId)
                .findFirst().orElse(null);
if (!Objects.isNull(recommendSchoolClass)){
            schoolClasses.add(recommendSchoolClass);
            schoolClassList.remove(recommendSchoolClass);
            schoolClasses.addAll(schoolClassList);
}
log.info("classes sorted result:{}", schoolClasses);
//对查到的集合进行过滤，如果是小学，则1-6年级为有效，如果是初中，则7-9年级为有效
List<SchoolClass> availableSchoolClassList = schoolClasses.stream().filter(schoolClass ->
                GradeUtils.isClassAvailable(schoolClass.getGrade(), 
                schoolClass.getGradeStage())).collect(Collectors.toList());

此段代码，if判断后没有考虑else的情况，导致集合schoolClasses 可能是empty。

避免此情况可以追加else处理相同逻辑。