I'm trying to make a POS using javaFX but whenever I try to change the scene it keeps crasing. Any ideas of how to fix?

Main class: <https://pastebin.com/4bspSL9N>

SceneManager: <https://pastebin.com/SU99DVgf>

OutputHelper.log() is just a `system.out.println()`

output log: <https://pastebin.com/GZTPRgNp>