What is wrong with my relationships JPA?

Question

I'm trying to create a back-end forum using JPA to interact with the database.. The problem that I'm facing now is the relationships between entities. I have 3 of them (at least for now) but when I try to create the tables using the JPA tools, it doesn't create them all which makes me think that there's something wrong with the relationships. Can anyone help me?

@Entity
@Table(name="users")
public class UserModel {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long user_id;
    private String name;
    private String email;
    @OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST,CascadeType.MERGE})
    private ArrayList<TopicoModel> myTopics = new ArrayList<TopicoModel>();

    @ManyToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST,CascadeType.MERGE})
    private ArrayList<TopicoModel> myFavTopics = new ArrayList<TopicoModel>();

--

@Entity
@Table(name="topics")
public class TopicModel{

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long topic_id;

    @OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST,CascadeType.MERGE})
    private ArrayList<PostModel> comments;

    @ManyToOne(cascade = CascadeType.MERGE)
    private UserModel author;

--

@Entity
@Table(name="posts")
public class PostModel {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long post_id;

    private String message;
    private int likes = 0;
    private int dislikes = 0;
    @OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST,CascadeType.MERGE})
    private ArrayList<UserModel> agrees;
    @OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST,CascadeType.MERGE})
    private ArrayList<UserModel> thanks;

EDIT1: When I try to populate the db with some test data its gives me the following error:

Internal Exception: java.sql.SQLException: Field 'myTopics_TOPIC_ID' doesn't have a default value
Error Code: 1364
Call: INSERT INTO users_topics (myFavTopics_TOPIC_ID, UserModel_USER_ID) VALUES (?, ?)
    bind => [2 parameters bound]
Query: DataModifyQuery(name="topicos_favoritos" sql="INSERT INTO users_topics (myFavTopics_TOPIC_ID, UserModel_USER_ID) VALUES (?, ?)")

EDIT2: I already tried to add a default value but it gives me the same error but with "myFavTopics" variable. Here is the code to populate the db:

UserModel u1 = new UserModel();
u1.setEmail("asd@asd.pt");
u1.setName("A");

UserModel u2 = new UserModel();
u2.setEmail("qwer@qwer.pt");
u2.setName("B");

PostModel p1 = new PostModel("message 1", 0, 0);
PostModel p2 = new PostModel("message 2", 10, 0);
PostModel p3 = new PostModel("message 3", 0, 20);

ArrayList<PostModel> commentP1 = new ArrayList<PostModel>();
commentP1.add(p1);
commentP1.add(p3);

ArrayList<PostModel> commentP2 = new ArrayList<PostModel>();
commentP2.add(p2);


TopicModel t1 = new TopicModel(commentP1, u1);
TopicModel t2 = new TopicModel(commentP2, u2);

u1.addMyTopic(t1);
u2.addMyTopic(t2);

u1.addMyFavTopic(t2);


UserModel u3 = new UserModel();
u3.setEmail("yujy@yj.pt");
u3.setName("C");

JPAEntityManager factory = new JPAEntityManager();
EntityManager em = factory.getEntityManager();

em.getTransaction().begin();
em.persist(t1);
em.persist(t2);
em.persist(p1);
em.persist(p2);
em.persist(p3);
em.persist(u1);
em.persist(u2);
em.persist(u3);

em.getTransaction().commit();