yet another problem with kivy

yap.py

from kivy.uix.label import Label
from kivy.uix.image import Image
from kivy.uix.stacklayout import StackLayout
from kivy.app import Builder, App

class MyApp(App):
    def build(self):
        
        lay1 = StackLayout(size_hint_y=None)
        lay1.bind(minimum_height = lay1.setter("height"))
          
        img = Image()
        lay1.add_widget(img)
          
        lbl = Label(text="test")
        lay1.add_widget(lbl)
          
        return lay1

MyApp().run()