protected function appendSingleFormFields(FormBuilderInterface $formBuilder)
    {
        $defaultOptions = [
            'label'    => $this->getTitle(),
            'required' => false,
        ];

        $userOptions = array_key_exists('single', $this->getFormOptions())
            ? $this->getFormOptions()['single']
            : [];

        if (count($userOptions) > 0) {
            $defaultOptions = array_merge($defaultOptions, $userOptions);
        }

        $defaultOptions['property_path'] = 'value';

        $formBuilder->add($this->getValuePropertyName(), $this->getFormFieldType(), $defaultOptions);

        return $this;
    }