displayUsing not called on BelongsTo field when value is null

• Laravel Version: 12.20
• Nova Version: 5.7.4
• PHP Version: 8.2

Description:

The issue reported in https://github.com/laravel/nova-issues/issues/1901 was fixed for most Fields, but for BelongsTo fields it's not working, The displayUsing and resolveUsing methods differ between BelongsTo and the rest that extend Fields

Detailed steps to reproduce the issue on a fresh Nova installation:

example:

This does not work, displayUsing is never called when the value is null:

 BelongsTo::make('Vessel')
    ->sortable()
    ->searchable()
    ->rules('nullable', 'integer', 'exists:App\Models\Vessel,id')
    ->displayUsing(fn (?Vessel $vessel) => $vessel === null ? 'Global' : $vessel->id)
    ->hideFromIndex(fn (ResourceIndexRequest $request) => $request->viaRelationship())
    ->nullable()
    ->help('If not provided Role is global, i.e. available to be assigned any user on any vessels'),

but this does work, displayUsing is called whatever the value:

Text::make('test')->nullable()->displayUsing(fn (?string $test) => $test ?? 'Missing')

Reproduce the issue on a fresh Nova installation using the BelongsTo and Text examples in the report. Compare how displayUsing and resolveUsing handle null values for BelongsTo versus Text, then verify that the BelongsTo displayUsing callback is invoked for a null relationship and produces the expected display value.