Deny access.
A checker should return this value to indicate it does not grant access to
a route.
File
   - drupal/core/lib/Drupal/Core/Access/AccessCheckInterface.php, line 32
 
  - Contains Drupal\Core\Access\AccessCheckInterface.
 
  Class
  
  - AccessCheckInterface 
 
  - An access check service determines access rules for particular routes.
 
  Namespace
  Drupal\Core\Access
Code
const DENY = NULL;