case model.Vector:
		numSamples = v.Len()
	case model.Matrix:
		numSamples = v.Len()
	case *model.Scalar:
		numSamples = 1
	default:
		return fmt.Errorf("unknown metric value type: %T", v)
	}
	if includeQuery(query, excluded) {
		if numSamples == 0 {
			return fmt.Errorf("expected a metric value for '%s', found no samples: %#v", query, value)
		}
	} else {
		if numSamples != 0 {