if len(res) == 0 {
		return nil, fmt.Errorf("failed to find matching goroutines for name: %s", name)
	}
	return res, nil
}

// pprofMatchingRegions returns the time intervals of matching regions
// grouped by the goroutine id. If the filter is nil, returns nil without an error.
func pprofMatchingRegions(filter *regionFilter, t *parsedTrace) (map[trace.GoID][]interval, error) {
	if filter == nil {
		return nil, nil
	}