if判断条件中也要有顺序

List<Integer> projectids= projectServiceManagementService.listProjectByUserID(userid,usertype);
    if(  projectids.size()!=0 && projectids != null){
     projectLists = projectServiceManagementService.getProjectListbyIds(projectids);
    }

这段代码中会有bug，bug在于当projectids 为null的时候 projectids.size()这个地方已经报错了

所以正确的写法应该是   if(  projectids != null && projectids.size()!=0 )