Uno 7 migration guide does not mention that FrameworkElement.DataContext is now nullable (object?) #24875

On which page? 📄

https://platform.uno/docs/articles/migrating-to-uno-7.html (section "Members restricted to their WinUI declaring types", the DataContext entry, and migration checklist item 15)

What's wrong? ❗

The 7.0 guide explains that DataContext now lives on FrameworkElement only, but it does not mention that the property is now declared as nullable: public object? DataContext. Before, it was emitted by the DependencyObject source generator as a plain object (no nullable annotation).

The nullable annotation is the correct one (the default is null, and DataContext = null is valid), but it surfaces as new compiler warnings in code that was clean on 6.x:

FrameworkElement fe = ...;
object x = fe.DataContext;   // CS8600: Converting null literal or possible null value to non-nullable type
Foo(fe.DataContext);         // CS8604: Possible null reference argument (when Foo takes a non-nullable object)

For projects with <Nullable>enable</Nullable> and <TreatWarningsAsErrors>true</TreatWarningsAsErrors> (or <WarningsAsErrors>nullable</WarningsAsErrors>) this becomes a build break after the upgrade, with no hint in the guide. We hit it while retargeting a library to 7.0.0-dev.645 (CS8604 at a call site passing DataContext to a non-nullable parameter). The guide already documents a similar case for Uno0001 and TreatWarningsAsErrors, so there is precedent for a note.

Verified by code inspection on master (c83e458): src/Uno.UI/UI/Xaml/FrameworkElement.DataContext.cs declares public object? DataContext, and doc/articles/migrating-to-uno-7.md has no mention of nullable annotations or DataContext nullability.

Any feedback? 💬

Suggested addition to the DataContext bullet and checklist item 15: "FrameworkElement.DataContext is now annotated object?. With nullable reference types enabled, reads that flow into a non-nullable object produce CS8600/CS8604. Null-check, use !, or pattern-match (if (fe.DataContext is MyViewModel vm))."

Optionally, add a short general note that nullable annotation changes in 7.0 can surface as warnings in TreatWarningsAsErrors projects.