How to persist entity with auto increment Id

when create new entity class from database, if the primary key (for example "Id") with auto increment get annotation @NotNull. At this time, if you use entity manager try to persist an entity, neither set the Id value nor automaticly generate the Id.

Foe Example:

Employer e1 = new Employer();       
e1.setName(name);
em.persist(e1);

The above will get error

In the Employer entity class

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@NotNull.-----------------------------------------------------Delete it!!
@Basic(optional = false)
@Column(name = "ID")
private Integer id;

You will  fix the problem.