code: private function getExistingSubpaths(string $subpath): array
      {
          $paths = [];
  
          foreach ($this->paths as $path) {
              if (is_dir($dir = $path.'/'.$subpath)) {
                  $paths[] = $dir;
              }
          }
  
          if (empty($paths)) {
              throw new \InvalidArgumentException(sprintf('The subpath "%s" does not exists.', $subpath));
          }
  
          return $paths;
      }
docs: @throws \InvalidArgumentException
  
  @return string[]