toUrl method
Create the url for the current Avataaar data with all parameters needed.
Implementation
String toUrl() {
//https://avataaars.io required that the first letter must be capitalised. fixed keys and added the capitalization to value
final params = _pieceEntries.map((it) {
final key = it.key[0].toLowerCase() + it.key.substring(1);
final value = it.value[0].toUpperCase() + it.value.substring(1);
return '$key=$value';
}).join('&');
return '$baseUrl/?$params';
}