When a @OneToMany is of type Map and it has a @MapKey set this property is not automatically set when the map is saved via a cascade.

public class CommentLink {
...
    @OneToMany(cascade=CascadeType.ALL)
    @MapKey(name="title")
    Map comments;

In the below code.. the title is used in the key of the Map but it is not automatically set against the bean, and in the database can end up as null.

User u = (User)Ebean.getReference(User.class, 1);
		
CommentLink cl = new CommentLink();
cl.setLinkUrl("http://none");
		
Comment cm = new Comment();

// without this set... title can be null
//cm.setTitle("kumera");

cm.setBody("body2");
cm.setUser(u);
		

Map comments = new LinkedHashMap();
// title not automatically set from the key value
comments.put("kumera", cm);

cl.setComments(comments);

Ebean.save(cl);