Ok I found out solution. I have to pass to concstuctor of ValidationError first argument as empty string. So whole code looks like:
public static class LoginForm {
@Constraints.Required
public String email;
@Constraints.Required
public String password;
public List<ValidationError> validate() {
List<ValidationError> errors = new ArrayList<ValidationError>();
User user = User.findByEmail(email);
if (user == null || !Hash.checkPassword(password, user.passwordHash)) {
errors.add(new ValidationError("", "Invalid email"));
return errors;
} else if (!user.validated) {
errors.add(new ValidationError("", "Not validated email"));
return errors;
}
return null;
}
}