normalize method
Implementation
String normalize(String field) {
String normalizedField = field;
substitutions.forEach((pattern, replacement) {
normalizedField = normalizedField.replaceAll(RegExp(pattern, caseSensitive: false), replacement);
});
normalizedField = normalizedField.replaceAll(RegExp(r'[^\w\s]'), '');
return normalizedField.split(' ').where((s) => s.isNotEmpty).join(' ').toLowerCase();
}