getItem method
Function that will retrieve a single json object from the database.
Implementation
Future<Map<String, dynamic>?> getItem(String key) async {
final Database db = await _databaseFuture;
final List<Map<String, dynamic>> queryResult =
await db.query(_table, where: 'key = ?', whereArgs: [key]);
return _processQueryResult(key, queryResult, db);
}