ArgumentNullException: Value cannot be null. (Parameter 's')

Question

I am trying to pull data from the table which has a DateTime data type with NULL values.
I am trying to get the required data by using the below method. However, it's throwing an error : ArgumentNullException: Value cannot be null. (Parameter 's')

TermDate = s.TermDate.HasValue ? s.TermDate : DateTime.Parse(s.TermDate.ToString().Replace(null, "-"))
 

Property: public DateTime? TermDate { get; set; }

Please advise.