【Flutter環境構築】Undefined name 'Encoding'. Try correcting the name to one that is defined

final uri = Uri.dataFromString(
  html,
  mimeType: 'text/html',
  encoding: Encoding.getByName('utf-8'),
);

import 'dart:convert' ;
    
// 省略

final uri = Uri.dataFromString(
  html,
  mimeType: 'text/html',
  encoding: Encoding.getByName('utf-8'),
);