On delete set null on update set null

Question

Hi, 

 

I have two tables called 

 University(Had Primary Key)

 Student

 

Here i am trying create fk on Student table with the condition ON UPDATE SET NULL ON DELETE SET NULL 

 

The following is an error.

 

Msg 1761, Level 16, State 0, Line 1

Cannot create the foreign key "fk_on_Student" with the SET NULL referential action, because one or more referencing columns are not nullable.

Msg 1750, Level 16, State 0, Line 1

Could not create constraint. See previous errors.