Bevy Ui Crash

main.rs

use bevy::prelude::*;

pub struct GlobalChildRef(pub Entity);
pub struct GlobalChild;

fn setup(
    mut commands: Commands,
    mut materials: ResMut<Assets<ColorMaterial>>,
    global_child: ResMut<GlobalChildRef>,
) {
    // the code below crashes.

    commands
        .spawn(UiCameraComponents::default())
        .spawn(NodeComponents::default())
        .with_children(|parent| {
            parent
                .spawn_as_entity(
                    global_child.0,
                    NodeComponents {
                        style: Style {
                            size: Size::new(Val::Px(40.0), Val::Px(40.0)),
                            position: Rect {
                                top: Val::Px(100.0),
                                left: Val::Px(100.0),
                                ..Default::default()
                            },
                            ..Default::default()
                        },
                        material: materials.add(ColorMaterial::color(Color::RED)),
                        ..Default::default()
                    },
                )
                .with(GlobalChild);
        });
}

/// Move the child entity from 100, 100 to 30, 30
fn move_child_entity_around(
    global_child_ref: Res<GlobalChildRef>,
    global_child_query: Query<(Entity, &GlobalChild, &mut Style)>,
) {
    let global_child_entity = global_child_ref.0;
    let mut global_child_style = global_child_query.get_mut::<Style>(global_child_entity).unwrap();

    global_child_style.position = Rect {
        top: Val::Px(30.0),
        left: Val::Px(30.0),
        ..Default::default()
    };
}

fn main() {
    App::build()
        .add_resource(GlobalChildRef(Entity::new()))
        .add_default_plugins()
        .add_startup_system(setup.system())
        .add_system(move_child_entity_around.system())
        .run();
}