TabViewItem without header set causes crash

Describe the bug

The following code will cause a crash on launch:

<muxc:TabView x:Name="rootTabView">
    <muxc:TabView.TabItems>
        <muxc:TabViewItem>
            <!--<muxc:TabViewItem.Header>
                <TextBlock Text="Without me, you'll crash" />
            </muxc:TabViewItem.Header>-->
            <muxc:TabViewItem.Content>
                <Button Content="I should be in the content area" />
            </muxc:TabViewItem.Content>
        </muxc:TabViewItem>
    </muxc:TabView.TabItems>
</muxc:TabView>

Uncommenting out the Header set will avoid the crash. Having a Header should not be a hard requirement for TabViewItem; it should render blank if not set.

Steps to reproduce the bug

Steps to reproduce the behavior: See above markup.

The error is cryptic:

Expected behavior

No crash.

Screenshots

Version Info

NuGet package version:

[Microsoft.UI.Xaml 2.6.1] - latest stable

Windows version	Saw the problem?
Insider Build (22000)	Yes
October 2020 Update (19042)
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

[zadjii-msft]

(not to help triage your repo or anything, but with #3426 merged, should this one be closed too?)

[chingucoding]

The PR @StephenLPeters linked looks good to me and ready to merge.