first method
Return first matching entity or null.
Implementation
Future<T?> first() async {
final finder = Finder(
filter: _filters.isEmpty
? null
: _filters.length == 1
? _filters.single
: Filter.and(_filters),
sortOrders: _sortOrders.isEmpty ? null : _sortOrders,
limit: 1,
offset: _offset,
);
final maps = await _source.collection.findWithFinder(finder);
if (maps.isEmpty) return null;
return _source.mapFromMaps(maps).first;
}