求了句linq写法，关于条件查询的，isnull解决思路

求了句linq写法，关于条件查询的，isnull
var q = db.company_job.Count(u => u.sate == true && u.selectjob == Convert.ToInt32(rselectjob3.SelectedValue));

如何改成下面这句？
from company_job where selectjob=isnull(@selectjob,selectjob) and sate =1

谢谢

[解决办法]
var q = db.company_job.Count(u => u.sate == true 
&& u.selectjob == (Convert.ToInt32(rselectjob3.SelectedValue) == xxx ? u.selectjob : Convert.ToInt32(rselectjob3.SelectedValue)));


????