NullArgument.php

<?php

namespace Drupal\views\Plugin\views\argument;

use Drupal\Core\Form\FormStateInterface;

/**
 * Argument handler that ignores the argument.
 *
 * @ingroup views_argument_handlers
 *
 * @ViewsArgument("null")
 */
class NullArgument extends ArgumentPluginBase {
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['must_not_be'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * Override buildOptionsForm() so that only the relevant options
     * are displayed to the user.
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['must_not_be'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Fail basic validation if any argument is given'),
            '#default_value' => !empty($this->options['must_not_be']),
            '#description' => $this->t('By checking this field, you can use this to make sure views with more arguments than necessary fail validation.'),
            '#group' => 'options][more',
        ];
        unset($form['exception']);
    }
    
    /**
     * Override defaultActions() to remove actions that don't
     * make sense for a null argument.
     */
    protected function defaultActions($which = NULL) {
        if ($which) {
            if (in_array($which, [
                'ignore',
                'not found',
                'empty',
                'default',
            ])) {
                return parent::defaultActions($which);
            }
            return;
        }
        $actions = parent::defaultActions();
        unset($actions['summary asc']);
        unset($actions['summary desc']);
        return $actions;
    }
    
    /**
     * Override the behavior of query() to prevent the query
     * from being changed in any way.
     */
    public function query($group_by = FALSE) {
    }

}