code: func (l *Log) tableRef(ctx context.Context) (string, error) {
  	projID := l.projID(ctx)
  	if projID == "" || strings.ContainsRune(projID, '/') {
  		return "", fmt.Errorf("invalid project ID %q", projID)
  	}
  	if l.DatasetID == "" || strings.ContainsRune(l.DatasetID, '/') {
  		return "", fmt.Errorf("invalid dataset ID %q", l.DatasetID)
  	}
  	if l.TableID == "" || strings.ContainsRune(l.TableID, '/') {
  		return "", fmt.Errorf("invalid table ID %q", l.TableID)
  	}
  	return fmt.Sprintf("%s/%s/%s", projID, l.DatasetID, l.TableID), nil
  }
docs: // tableRef returns an identifier of the table in BigQuery.
  //
  // Returns an error if Log is misconfigred.