You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: normalize_label.go
    path of file: ./repos/prometheus/storage/remote/otlptranslator/prometheus
    
    the code of the file until where you have to start completion: // DO NOT EDIT. COPIED AS-IS. SEE ../README.md

// Copyright The OpenTelemetry Authors
// SPDX-Lic
    
func NormalizeLabel(label string) string {

	// Trivial case
	if len(label) == 0 {
		return label
	}

	// Replace all non-alphanumeric runes with underscores
	label = strings.Map(sanitizeRune, label)

	// If label starts with a number, prepend with "key_"
	if unicode.IsDigit(rune(label[0])) {
		label = "key_" + label
	} else if strings.HasPrefix(label, "_") && !strings.HasPrefix(label, "__") && !dropSanitizationGate.IsEnabled() {
		label = "key" + label
	}

	return label
}