code: public function getChildRoles($roleName)
      {
          $role = $this->getRole($roleName);
  
          if ($role === null) {
              throw new InvalidArgumentException("Role \"$roleName\" not found.");
          }
  
          $result = [];
          $this->getChildrenRecursive($roleName, $this->getChildrenList(), $result);
  
          $roles = [$roleName => $role];
  
          $roles += array_filter($this->getRoles(), function (Role $roleItem) use ($result) {
              return array_key_exists($roleItem->name, $result);
          });
  
          return $roles;
      }
docs: {@inheritdoc}