load method
Loads environment variables from the env file into a map
Merge with any entries defined in mergeWith
Implementation
Future<void> load(
{String fileName = '.env', Parser parser = const Parser(), Map<String, String> mergeWith = const {}}) async {
clean();
final linesFromFile = await _getEntriesFromFile(fileName);
final linesFromMergeWith = mergeWith.entries.map((entry) => "${entry.key}=${entry.value}").toList();
final allLines = linesFromMergeWith..addAll(linesFromFile);
final envEntries = parser.parse(allLines);
_envMap.addAll(envEntries);
_isInitialized = true;
}