Does JPA return "null" or empty collection for a collection property that is empty in the DB?

Question

If I have a JPA entity containing a collection field, such as

public class Post {    
  // [...]
  @OneToMany
  private List<String> tags;

the corresponding database schema will typically contain a separate table for storing the tags, where each record contains one tag and a foreign key reference to the "Post" table.

Now when I load a "Post" entity from the database which has no tags (i.e. no corresponding "tag" records exist), what will the value of Post.tags be? Will it be set to null, or to an empty List? Or is this undefined?

I could not find this in the JPA specification.

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Note: This is the same question like Does Hibernate return null or empty collection if table in relation is empty?, only for the JPA spec instead of for Hibernate specifically.

I know that most JPA implementations (at least Hibernate and EclipseLink) will return an empty collection - I'm interested in whether this is specified anywhere.

Answer 1

According to the JPA 2.1 spec:

2.9 Entity Relationships

If there are no associated entities for a multi-valued relationship of an entity fetched from the database, the persistence provider is responsible for returning an empty collection as the value of the relationship.