Fatal error: Call to a member function Services() on null

it's correct?
Member::get()->byId($this->urlParams['ID'])->Services()->map('Title','Title')
thanks for the help!

class MemberProfileViewer extends Page_Controller {

    // ...

public function form() {

    $fields = new FieldList(
        CheckboxSetField::create(
            $name = "ServiceID",
            $title = "Select",
            $source = Member::get()->byId($this->urlParams['ID'])->Services()->map('Title','Title')
        ),
    )

    $actions = FieldList::create(
            FormAction::create('form', 'Send')
                ->setUseButtonTag(true)
                ->addExtraClass('btn btn-primary')
    );

    $validator = new RequiredFields('ServiceID');

    $form = new Form($this, 'form', $fields, $actions, $validator);
    $form->setFormMethod('POST', true);
    return $form;
}

public function doform($data, $form) {
    $form->sessionMessage(
        "Thank you, you will be contacted as soon as possible by our consultant.", 'good'
    );

    $submission = new RequestForm();
    $form->saveInto($submission);
    $submission->write();

    return $this->redirectBack();

}