#Most important error in EF code first

1. Introducing FOREIGN KEY constraint 'FK_dbo.xxx_dbo.Employee_xxx' on table 'xxx' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint. See previous errors.

if you get this error add ? on that property
```
  public int? StudentID { get; set; }
```