better query checking before redirect

src/Controller/RoblibSearchController.php

@@ -3,8 +3,9 @@
 namespace Drupal\roblib_search\Controller;
 
 use Drupal\Core\Controller\ControllerBase;
-use \Drupal\Core\Url;
+use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\RedirectResponse;
+use Drupal\Component\Utility\Html;
 
 /**
  * Controller for d3 graphs.
@@ -19,7 +20,14 @@ class RoblibSearchController extends ControllerBase {
    */
   public function searchResults($query = NULL) {
     if ($query = $_GET['roblib_query']) {
+      $query = str_replace('/', ' ',$query);
+      $query = trim(Html::decodeEntities($query));
+      if(empty($query)) {
+        \Drupal::messenger()->addMessage($this->t('Please Enter a valid search string.'));
+        $url = Url::fromRoute('roblib_search.landing_page');
+      } else {
         $url = Url::fromRoute('roblib_search.landing_page', ['query' => $query]);
+      }
       return new RedirectResponse($url->toString());
     }
      return [