Repository: flutter
Issue: [two_dimensional_scrollables] TreeView Widget blanks when closing last parent
Labels: package,a: desktop,has reproducible steps,P2,team-framework,triaged-framework,p: two_dimensional_scrollables,found in release: 3.22,found in release: 3.23

### Steps to reproduce

1. Open a TreeView such that all Elements exceeds screensize height
2. Scroll down to the latest Item. This Item should be a parent of other items
3. Open the item and then close it.

Failure is also reproducable with the given example from the library.

Tested on Linux and Windows

### Expected results

The item should close normally.

### Actual results

The whole tree disappears and i get the following exception. After scrolling up and down the tree reappears.

``` console
The following _TypeError was thrown during paint():
Null check operator used on a null value

The relevant error-causing widget was: 
  TreeView<WorkPackage> TreeView:file:///<projectpathfile>
When the exception was thrown, this was the stack: 
#0      RenderTreeViewport._paintRows (package:two_dimensional_scrollables/src/tree_view/render_tree.dart:594:8)
#1      RenderTreeViewport.paint.<anonymous closure> (package:two_dimensional_scrollables/src/tree_view/render_tree.dart:422:13)
#2      PaintingContext.pushLayer (package:flutter/src/rendering/object.dart:486:12)
#3      PaintingContext.pushClipRect (package:flutter/src/rendering/object.dart:546:7)
#4      RenderTreeViewport.paint (package:two_dimensional_scrollables/src/tree_view/render_tree.dart:417:57)
#5      RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:3239:7)
#6      PaintingContext._repaintCompositedChild (package:flutter/src/rendering/object.dart:166:11)
#7      PaintingContext.repaintCompositedChild (package:flutter/src/rendering/object.dart:109:5)
```


### Code sample

<details open><summary>Code sample</summary>

```dart
// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

import 'custom_tree.dart';
import 'simple_tree.dart';

/// The page containing the interactive controls that modify the sample
/// TreeView.
class TreeExplorer extends StatefulWidget {
  /// Creates a screen that demonstrates the TreeView widget in varying
  /// configurations.
  const TreeExplorer({super.key});

  @override
  State<TreeExplorer> createState() => _TreeExplorerState();
}

/// Which example is being displayed.
enum TreeType {
  /// Displays TreeExample.
  simple,

  /// Displays CustomTreeExample.
  custom,
}

class _TreeExplorerState extends State<TreeExplorer> {
  final SizedBox _spacer = const SizedBox.square(dimension: 20.0);
  TreeType _currentExample = TreeType.simple;
  String _getTitle() {
    return switch (_currentExample) {
      TreeType.simple => 'Simple TreeView',
      TreeType.custom => 'Customizing TreeView',
    };
  }

  Widget _getTree() {
    return switch (_currentExample) {
      TreeType.simple => const TreeExample(),
      TreeType.custom => const CustomTreeExample(),
    };
  }

  Widget _getRadioRow() {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Row(
        children: <Widget>[
          const Spacer(),
          Radio<TreeType>(
            value: TreeType.simple,
            groupValue: _currentExample,
            onChanged: (TreeType? value) {
              setState(() {
                _currentExample = value!;
              });
            },
          ),
          const Text('Simple'),
          _spacer,
          Radio<TreeType>(
            value: TreeType.custom,
            groupValue: _currentExample,
            onChanged: (TreeType? value) {
              setState(() {
                _currentExample = value!;
              });
            },
          ),
          const Text('Custom'),
          const Spacer(),
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(_getTitle()),
        bottom: PreferredSize(
          preferredSize: const Size.fromHeight(50),
          child: Padding(
            padding: const EdgeInsets.all(8.0),
            child: _getRadioRow(),
          ),
        ),
      ),
      body: _getTree(),
    );
  }
}
```

</details>


### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>




https://github.com/flutter/flutter/assets/6066475/c4886475-2f84-4548-842f-8bfd04a83107


https://github.com/flutter/flutter/assets/6066475/b02dd4db-b7ad-4fb7-838d-d444d70b81ad









</details>


### Logs

_No response_

### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.22.1, on Manjaro Linux 6.8.9-3-MANJARO, locale de_DE.UTF-8)
[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
[✓] Chrome - develop for the web
[✓] Linux toolchain - develop for Linux desktop
[✓] Android Studio (version 2023.3)
[✓] Connected device (2 available)
[✓] Network resources

• No issues found!

```

</details>