Unable to Pass Null Value in Json - MVC Controller - json

Question

System is not passing 'null' value if there is no value for
model.SpecialtyTypeDesc = spec.SpecialtyDescription;
I am unable to open the edit page if there is no value for Specialty for the employee. If the employee has specificity value, its working fine. I want to display the value as Null if the employee doestn't have any specialty in his personnel data.
public JsonResult GetSpecialityDepartment(int id){
EmployeeDepartments getDep = (from c in db.EmployeeDepartments where c.EmpId == id select c).FirstOrDefault();
Departments dept = (from c in db.Departments where c.Id == getDep.departmentId select c).FirstOrDefault();
EmployeeDetails details = (from c in db.EmployeeDetails where c.People_Id == id select c).FirstOrDefault();
SpecialtyType spec = (from c in db.SpecialityType where c.SpecialtyTypeId == details.SpecialtyTypeId select c).FirstOrDefault();
var data = new {
Department = dept.Name,
SpecialtyType = spec == null ? "" : spec.SpecialtyDescription
};
return Json(data);
}
public ActionResult Edit(int id) {
PersonnelLeaveAbsence leaveAbsence = (from c in db.PersonnelLeaveAbsence where c.PersonnelLeaveAbsenceId == id select c).FirstOrDefault();
EmployeeDepartments getDep = (from c in db.EmployeeDepartments where c.EmpId == leaveAbsence.PersonnelId select c).FirstOrDefault();
Departments dept = (from c in db.Departments where c.Id == getDep.departmentId select c).FirstOrDefault();
EmployeeDetails details = (from c in db.EmployeeDetails where c.People_Id == leaveAbsence.PersonnelId select c).FirstOrDefault();
SpecialtyType spec = (from c in db.SpecialtyType where c.SpecialtyTypeId == details.SpecialtyTypeId select c).FirstOrDefault();
PersonnelLeaveAbsenceModel model = new PersonnelLeaveAbsenceModel();
model.PersonnelLeaveAbsenceId = leaveAbsence.PersonnelLeaveAbsenceId;
model.PersonnelLeaveDate = leaveAbsence.LeaveDate;
model.LeaveAbsenceId = leaveAbsence.LeaveAbsenceTypeId;
model.PersonnelId = leaveAbsence.PersonnelId;
model.EmployeeRoleId = leaveAbsence.EmployeeRole;
model.StartTime = leaveAbsence.StartTime;
model.EndTime = leaveAbsence.EndTime;
model.DayType = Convert.ToBoolean(leaveAbsence.DayType);
model.DepartmentDesc = dept.Name;
model.SpecialtyTypeDesc = spec.SpecialtyDescription;
}