update

TEAMModelOS/Controllers/Both/CourseBaseController.cs

@@ -2142,6 +2142,10 @@ namespace TEAMModelOS.Controllers.Both
                 {
                     var school = schools.Find(z => z.id.Equals(course.school));
                     var period = school.period.Find(z => z.id.Equals(course.period?.id));
+                    if(period==null)
+                    {
+                        continue;
+                    }
                     var semester = SchoolService.GetSemester(period, course._ts.Value);
                     CourseBase courseBase = new CourseBase()
                     {