private function readStoredRoutineMetadata(): void
  {
    if (file_exists($this->phpStratumMetadataFilename))
    {
      $this->phpStratumMetadata = (array)json_decode(file_get_contents($this->phpStratumMetadataFilename), true);
      if (json_last_error()!=JSON_ERROR_NONE)
      {
        throw new RuntimeException("Error decoding JSON: '%s'.", json_last_error_msg());
      }
    }
  }