code: public function getCombinationsForUser($userGroups, $userType)
      {
          $userType = strtolower($userType);
          if ('fe' !== $userType && 'be' !== $userType) {
              throw new \InvalidArgumentException('Unknown user type: ' . $userType);
          }
  
          return $this->getCombinationsFromDatabase($userGroups, $userType);
      }
docs: Retrieve the combinations for the passed user.
  
  @param string[] $userGroups The user groups.
  @param string   $userType   The user type ('fe' or 'be').
  
  @return array|null
  
  @throws \InvalidArgumentException When the user type is unknown.