how to handle null value while getting image in asp.net

Question

Session["EmpPhoto"] = dsUser.Tables[0].Rows[0]["EmpPhoto"].ToString();

 

imageUser.ImageUrl = Session["Photo"].ToString();//here i am getting error 

 

i have to       show username and userphoto after he logged into the site. but for a particular user i dont have image so i am getting error" Object reference not set to an instance of an object.

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