Error when initializing DockLayout with nonempty windowbox

[rayman-de]

When the initial layout passed as prop to a DockLayout has children in its windowbox, an error is thrown in NewWindow.openChild:

ERROR
Cannot read properties of null (reading 'left')
TypeError: Cannot read properties of null (reading 'left')
at NewWindow.openChild (http://localhost:3000/static/js/bundle.js:21972:7)
at NewWindow.componentDidMount (http://localhost:3000/static/js/bundle.js:21937:10)
at commitLayoutEffectOnFiber (http://localhost:3000/static/js/bundle.js:51397:34)
at commitLayoutMountEffects_complete (http://localhost:3000/static/js/bundle.js:52564:13)
at commitLayoutEffects_begin (http://localhost:3000/static/js/bundle.js:52553:11)
at commitLayoutEffects (http://localhost:3000/static/js/bundle.js:52499:7)
at commitRootImpl (http://localhost:3000/static/js/bundle.js:54409:9)
at commitRoot (http://localhost:3000/static/js/bundle.js:54289:9)
at finishConcurrentRender (http://localhost:3000/static/js/bundle.js:53686:13)
at performConcurrentWorkOnRoot (http://localhost:3000/static/js/bundle.js:53537:11)

This happens both with controlled and uncontrolled layouts.