TreeViewItem: Throw exception when ItemTemplate is misconfigured

[Taylan2020]

Description

I'm creating this PR in reference to my previously deleted PR #8168.

@henon fix is now ready to merge for v7. Thanks.

This TreeView-bug only occurs when TreeView.ServeData is used with a custom ItemTemplate.

The parent node reference passed to the MudTreeView.ServerData delegate function is ALWAYS null when the parameter > 'Value' is NOT set in the customized MudTreeViewItems-Template. To fix this issue an exception is thrown when the parameter

MudTreeView.ServerData is set with MudTreeViewItem.Value & > MudTreeViewItem.Text unset.

MudTreeView.Text needs to be null to make sure the TreeViewItem is not only supplied with a display text - in which case the parentNode would be null anyways.

See Ticket #7156 for bug reproduction - still present in latest release v6.0.15.

How Has This Been Tested?

Unit test is included in the comit covering the same scenario from Ticket #7156.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.13%. Comparing base (28bc599) to head (5819059).
Report is 135 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8867      +/-   ##
==========================================
+ Coverage   89.82%   90.13%   +0.30%     
==========================================
  Files         412      421       +9     
  Lines       11878    12304     +426     
  Branches     2364     2431      +67     
==========================================
+ Hits        10670    11090     +420     
+ Misses        681      665      -16     
- Partials      527      549      +22     

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[henon]

@Taylan2020 for a && b && c you don't need brackets.

@ScarletKuro is this OK or should we use the state framework for this?

[ScarletKuro]

I guess it's fine for this case.

[henon]

In principle this is mergable. I just want to get a second opinion from @ScarletKuro

[henon]

lol, while searching for the the thing to fix I stumbled accross this:

        protected override async Task OnInitializedAsync()
        {
            if (Parent != null)
            {
                Parent.AddChild(this);
            }
            else
            {
                if (MudTreeRoot is not null)
                {
                    await MudTreeRoot.AddChildAsync(this);
                }
            }
            base.OnInitialized();
        }

OnInitializedAsync() calls base.OnInitialized()

Guess that was an oversight by me in an earlier PR

[henon]

Thanks @Taylan2020 !