TextInput crashes in open() method

main.py

from text_editor import TextEditorPopup
from kivy.core.window import Window
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.app import App

class TApp(App):
    def build(self):
        root = Label(text='Press "Enter" to open TextInput')
        Window.bind(on_key_down=self.on_key_down2)
        return root

    def on_key_down2(self, *args):
        if args[1] == 13:
            self.open_editor()

    def open_editor(self):
        popup = TextEditorPopup(text='')
        popup.open()


app = TApp()
app.run()

texteditor.py

from kivy.properties import StringProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.popup import Popup
from kivy.lang import Builder
from kivy.clock import Clock


Builder.load_string('''
<TextEditor>:
    orientation: 'vertical'
    TextInput:
        id: input
        multiline: True
        font_size: 14
''')


class TextEditor(BoxLayout):
    pass


class TextEditorPopup(Popup):
    text = StringProperty()
    title = 'Text editor'

    def __init__(self, **kwargs):
        super(TextEditorPopup, self).__init__(**kwargs)
        self.content = TextEditor()

    def open(self, *args):
        super(TextEditorPopup, self).open(*args)
        self.content.ids.input.text = self.text
        self.content.ids.input.focus = True
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