Have you tried adding custom setters?
@Entity
public class User extends Model {
@Id
@Constraints.Min(10)
public Long id;
@Constraints.Required
public String username;
public void setUsername(String _username) {
username = _username;
}
@Constraints.Required
public String password;
public void setPassword(String _password) {
password = _password;
}
public static Finder<Long, User> find = new Finder<Long, User>(
Long.class, User.class
);
}