Flutter 颤振-将对象转换为可编码对象失败

我有一个发行人。请帮帮我。非常感谢

错误：将对象转换为可编码对象失败：“FutureBuilder”的实例

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包括您得到的错误。请阅读以下内容：

 Future<List<FtsMainContent>> querySearchWord(String word) async {
    final db = await ConectionDB.dbPro.database;
    HistoryTable his = HistoryTable();
    List<Map<String, dynamic>> maps =
        await db.rawQuery('select * from $tableName where origin = ?', [word]);
    return maps.map((e) => FtsMainContent.fromJson(e)).toList();
  } 

  Future<List<FtsMainContent?>> getSearchWord(String word) async {
    List<FtsMainContent> data = await fts.querySearchWord(word);
    return data;
  }

 return FutureBuilder(
    future: ftsPr.getSearchWord(word),
    builder: (context, snapshot) {
        ..................
        return Text('test');
    },
 );