Window title isn't inferred correctly from ui.panel_title()

[cpsievert]

from shiny import *

app_ui = ui.page_fluid(
    ui.panel_title("Hello Shiny UI"),
)

def server(input: Inputs, output: Outputs, session: Session):
    pass

app = App(app_ui, server)

Generates the warning:

/Users/cpsievert/github/py-shiny/shiny/ui/_page.py:138: UserWarning: Unable to infer a `window_title` default from `title`. Consider providing a character string to `window_title`.
  warn(

And the title isn't populated in the tab's title