find<T extends RealmObject>  method 
Fast lookup for a RealmObject with the specified primaryKey.
Implementation
T? find<T extends RealmObject>(Object? primaryKey) {
  final metadata = _metadata.getByType(T);
  final handle = _handle.find(metadata.classKey, primaryKey);
  if (handle == null) {
    return null;
  }
  final accessor = RealmCoreAccessor(metadata, _isInMigration);
  var object = RealmObjectInternal.create(T, this, handle, accessor);
  return object as T;
}