instagram 강의에서 내용이 없이 사진을 게시할 시에

a라는 내용이 setUserContent에 계속 남아 저번 a를 반영하여 아무 내용이 없이 사진을 게시해도
똑같은 내용만 나오는데 이를 해결할 방법이 있을까요???
setUserContent(a)함수를 수정하거나 @override Widget build 부분의  setUserContent(text) 부분을
if 함수로 변경하면 null<->string 비호환 경고 구문이 나와 이틀째 고생이네요. 하단은 지금까지 코딩한
내용입니다. 항상 양질의 강의 감사합니다.

import 'package:flutter/material.dart';
import 'package:instagram/style.dart' ;
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'package:flutter/rendering.dart';
import 'package:image_picker/image_picker.dart';
import 'dart:io';

void main() {
  runApp(MaterialApp(
    theme: theme,
    home: MyApp(),
  ));
}

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  var tab = 0;
  var data = [];
  var userImage;
  var userContent;

  addMyData(){
    var myData = {
      'id': data.length,
      'image': userImage,
      'likes': 5,
      'date': 'July 25',
      'content': userContent,
      'liked': false,
      'user': 'John Kim'
    };
    setState((){
      data.insert(0, myData);
    });
      }

  setUserContent(a){
    setState((){
      userContent = a;
    });
  }

  @override
  void initState() {
    super.initState();
    getData();

  }

  addData(a){
    setState((){
      data.add(a);
    });
  }

  getData() async {
    var result = await http.get(Uri.parse('https://codingapple1.github.io/app/data.json'));
    var result2 = jsonDecode(result.body);
    data = result2;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Instagram'),
        actions: [
          IconButton(
            icon: Icon(Icons.add_box_outlined),
            onPressed: () async {
              var picker = ImagePicker();
              var image = await picker.pickImage(source: ImageSource.camera);
              if(image != null){
                setState((){
                  userImage = File(image.path);

                });
              }

              Navigator.push(context,
                  MaterialPageRoute(builder: (c) => Upload(
                      userImage : userImage, setUserContent : setUserContent,
                      addMyData : addMyData,)
                  ));
            },
          )
        ],
      ),

      body: [bodyUI(data: data, addData : addData), Text('shop')]
,

      bottomNavigationBar: BottomNavigationBar(
          showSelectedLabels: false,
          showUnselectedLabels: false,
          onTap: (i){
            setState((){
              tab = i;
            });
          },
          items: [
            BottomNavigationBarItem(icon: Icon(Icons.home_outlined), label: 'home'),
            BottomNavigationBarItem(icon: Icon(Icons.shopping_bag_outlined), label: 'shop')
          ]),
      );
  }
}

class bodyUI extends StatefulWidget {
  const bodyUI({Key? key, this.data, this.addData}) : super(key: key);
  final data;
  final addData;

  @override
  State<bodyUI> createState() => _bodyUIState();
}

class _bodyUIState extends State<bodyUI> {

  var scroll = ScrollController();

  getMoreData() async {
    var result = await http.get(Uri.parse('https://codingapple1.github.io/app/more1.json'));
    var result2 = jsonDecode(result.body);
    widget.addData(result2);

  }

  @override
  void initState(){
    super.initState();
    scroll.addListener(() {
      if(scroll.position.pixels == scroll.position.maxScrollExtent){
        getMoreData();
      }
    });
  }

  @override
  Widget build(BuildContext context) {

    if(widget.data.isNotEmpty){

      return ListView.builder(itemCount: widget.data.length, controller: scroll, itemBuilder: (c, i){
        return Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            widget.data[i]['image'].runtimeType == String
                ? Image.network(widget.data[i]['image'])
                : Image.file(widget.data[i]['image']),
            Container(
              padding: EdgeInsets.all(20),
              width: double.infinity,
              constraints: BoxConstraints(maxWidth: 600),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text('좋아요 ${widget.data[i]['likes']}'),
                  Text(widget.data[i]['user']),
                  Text(widget.data[i]['content'])
                ],
              ),
            )
          ],
        );
      });
    } //if문 끝
    else {
      return Text('loading');
    }
  }

}

class Upload extends StatelessWidget {
  const Upload({Key? key, this.userImage, this.setUserContent, this.addMyData}) : super(key: key);
  final userImage;
  final setUserContent;
  final addMyData;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomInset: false,
      appBar: AppBar(
        actions: [
          IconButton(onPressed: (){
            addMyData();
            }, icon: Icon(Icons.send))
        ],
        leading: IconButton(onPressed: (){
          Navigator.pop(context);},
            icon: Icon(Icons.close)),
      ),
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Image.file(userImage,  height: MediaQuery.of(context).size.height - 500 ,
          alignment: Alignment.centerRight,),
          TextField(decoration: InputDecoration(labelText: '내용적기', prefixText: 'XOX'), onChanged: (text){
            setUserContent(text);
          }, ),
        ],
      ),
    );
  }

}