Select.Blank doesn't work on python 3.9

[Tim-Cao]

from textual.app import App, ComposeResult
from textual.containers import *
from textual.widgets import *
from textual import work


class ScriptApp(App):
    CSS = """
.unselected {
    display: none;
}

.unselected.visible {
    display: block;
}
"""

    def compose(self) -> ComposeResult:
        PROJECT_KEY = [
            ("LPS", "LPS"),
            ("LRQA", "LRQA"),
            ("LRAC", "LRAC"),
            ("COMMERCE", "COMMERCE"),
        ]

        yield Header()
        yield Label("Project Key:", id="project-key-label-2")
        yield Select(PROJECT_KEY, id="project-key-2")
        yield Label("Summary:", id="summary-label", classes="unselected")
        yield Input(id="summary", classes="unselected")
        yield Static()
        yield Button("Submit", id="button-7")
        yield Footer()

    @work(exclusive=True, thread=True)
    def create_issue(self) -> None:
        self.query_one("#button-7").disabled = True

        self.query_one("#summary").value = ""
        self.query_one("#project-key-2").clear()
        self.query_one("#button-7").disabled = False

    def on_button_pressed(self, event: Button.Pressed) -> None:
        if event.button.id == "button-7":
            self.create_issue()

    def on_select_changed(self, event: Select.Changed) -> None:
        self.query_one("#summary").set_class(event.value != Select.BLANK, "visible")
        self.query_one("#summary-label").set_class(
            event.value != Select.BLANK, "visible"
        )


app = ScriptApp()

if __name__ == "__main__":
    app.run()

When select an option in Project Key field, this error happened AttributeError: type object 'Select' has no attribute 'BLANK'

[TomJGooding]

Select.BLANK was added in Textual 0.42.0 - are you using an older version?

[Tim-Cao]

You're right. Thanks