Error 1 Cannot implicitly convert type 'long?' to 'long'. An explicit conversion exists (are you missing a cast?) 

  select new post

           {

           ID = r.ID,

          Title = r.Title,

          PostedDate = r.CreationDate,

       DeletedOn = r.ModificationDate,
                                                           

       ModifiedBy = r.ModifiedBy




      })

in modifiedBy its showing error of typecast

please help me