Ids for this class must be manually assigned before calling save on String ID

Already read lots of questions about the same issue, but I still not be able to solve this problem.

I need to have a String primary key on my database.

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class MyClass {

    @Id
    private String myId;
    private String name;

    // getters and setters..

}

The problem is that, if I use String type in a @Id annotated field, Hibernate throws an exception when I try to save the object.

ids for this class must be manually assigned before calling