NavigationRail is not shown if expand=True of parent is set in build method

[vodjan]

I hereby solemnly swear that I have read #287 and #303 and that what I am describing is, to my understanding, not covered by the solutions provided therein.

The following code results in an error, even though I am using a Row with expand=True to restrict the NavigationRail's height, as recommended in #303:

import flet as ft


class AppView(ft.UserControl):
    def __init__(self):
        super().__init__()
        self.navigation_rail = ft.NavigationRail(
            destinations=[
                ft.NavigationRailDestination(
                    icon=ft.icons.START,
                    label="one destination"
                ),
                ft.NavigationRailDestination(
                    icon=ft.icons.STAR,
                    label="another destination"
                )
            ],
            on_change=lambda event: print("Selected destination:", event.control.selected_index),
        )

    def build(self):
        return ft.Row(
            controls=[
                self.navigation_rail
            ],
            expand=True
        )


def main(page: ft.Page):
    app_view = AppView()
    page.add(app_view)


ft.app(target=main)

However, when I change main to wrap the NavigationRail in a Row with expand=True, the code works: both

def main(page: ft.Page):
    app_view = AppView()
    page.add(ft.Row([app_view], expand=True))

and

def main(page: ft.Page):
    app_view = AppView()
    page.add(ft.Row([app_view.navigation_rail], expand=True))

work just fine. These also work if I replace expand=True with height=200 in main.

Using an explicit height restriction in the build method also works fine, i.e.

class AppView(ft.UserControl):

...

    def build(self):
        return ft.Row(
            controls=[
                self.navigation_rail
            ],
            height=200
        )


def main(page: ft.Page):
    app_view = AppView()
    page.add(app_view)


ft.app(target=main)