Getting java.lang.IllegalStateException: org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl closed error while performing entity delete operation.

Sample code:

1.Group.java

@Entity
@Table(name = "user_group")
public class Group {
    ...
    @ManyToMany(fetch = FetchType.EAGER, cascade = {CascadeType.REMOVE})
    @JoinTable(name = "users_group_relation",joinColumns = @JoinColumn(name = "group_id"),inverseJoinColumns = @JoinColumn(name = "user_id")
    )
    private List<User> members;

}

User.java

@Entity
@Table(name = "users")
public class User {
    ...
    @ManyToMany(mappedBy = "members", cascade = {CascadeType.REMOVE})
    private List<Group> groups;

}

Delete operation code:

private void delete(int groupId) throws Exception {
        Transaction transaction = null;
        try (Session session = sessionFactory.openSession()) {
            transaction = session.beginTransaction();
            session.remove(groupId);
            transaction.commit();
            return result;
        } catch (Exception ex) {
            if (transaction != null) {
                transaction.rollback();
            }
            throw ex;
        }
    }

What is the problem here? And how to resolve this?