ListBox [Binding]An error occurred binding

[pzelektron]

This took me two days but accidentally I fixed it. But I'm still curious why this working.
This is my simple UserControl KatalogW it contains button and ItemsControl contains another instance of my control KatalogW.
When I press button to list is added new model for my control KatalogM and new control is display.
It displays something like treeview but branches are added only when I pres button.

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d" d:DesignWidth="400" d:DesignHeight="200"
             x:Class="PrzykladowyUserControlMVVM.Kontrolki.KatalogW"
			 xmlns:app="using:PrzykladowyUserControlMVVM.Kontrolki"
			 x:DataType="app:KatalogW"
			 x:Name="root">

	<StackPanel>
		<StackPanel.Styles>
			<Style Selector="ListBoxItem">
				<Setter Property="Padding" Value="0"/>
			</Style>
		</StackPanel.Styles>

		<Button	Command="{Binding #root.PobierzListeKatalogow}"
				Content="{Binding #root.ObecnyKatalog.NAZWA}"
				HorizontalAlignment="Stretch"
			    VerticalContentAlignment="Stretch"/>

		<ItemsControl
			ItemsSource="{Binding #root.ObecnyKatalog.ListaKatalogowPodrzednych}" Margin="20 0 0 0">
			<ItemsControl.ItemTemplate>
				<DataTemplate>
					<app:KatalogW ObecnyKatalog="{Binding }"/>
				</DataTemplate>
			</ItemsControl.ItemTemplate>
		</ItemsControl>
		
	</StackPanel>
	
</UserControl>

Button press Command:

    public void PobierzListeKatalogow()
    {
        ObecnyKatalog.ListaKatalogowPodrzednych.Add(new KatalogM() { NAZWA = "Katalog" + licznik++ });
    }

Class KatalogM contains only :

    public class KatalogM :ViewModelBase
    {
        public ObservableCollection<KatalogM> ListaKatalogowPodrzednych { get; set; } = [];

        private string _NAZWA = "";
        public string NAZWA
        {
            get => _NAZWA;
            set
            {
                _NAZWA = value; OnPropperytyChanged();
            }
        }
    }

And now the weird part. When I use :

<ListBox.ItemTemplate>

<app:KatalogW ObecnyKatalog="{Binding }"/>

</ListBox.ItemTemplate>

I get lot of this errors:

[Binding]An error occurred binding 'Content' to '#root.ObecnyKatalog.NAZWA' at 'ObecnyKatalog': 'Value is null.' (Button #50039568)
[Binding]An error occurred binding 'ItemsSource' to '#root.ObecnyKatalog.ListaKatalogowPodrzednych' at 'ObecnyKatalog': 'Value is null.' (ListBox #26673201)

But after switch to ItemsControl everything starts working. Why this happening ? And maybe I should change something in my model class code?