How to remove null values on button click?

Hi guys, I have a form with button "Select All Emails". Now the problem I have if I click the button it will display all emails in that "ContactEmail" field from the database, if there is no email created it will show "NULL". Now what I want is not to show anything if the field is null (no email created). Below my controller code;

 

public JsonResult GetAllUser(EmployeeModel objModelMail, string to)
{
        List Recyclers = new List();

        using (WasteRecyclersEntities db = new WasteRecyclersEntities())
         {
            var query = from q in db.Recyclers
            select q.ContactEmail;
            return new JsonResult { Data = query.ToList(), JsonRequestBehavior = JsonRequestBehavior.AllowGet };
         }

}