[BUG] Stack Trace error when joining the game

[Boopideedoo]

Round ID:

round ID:2321

TypeError: Unable to get property 'indexOf' of undefined or null reference
at isStyleSheetLoaded (http://127.0.0.1:59191/tgui-window-1.html:259:7)
at node.onload (http://127.0.0.1:59191/tgui-window-1.html:346:9)
User Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.2; WOW64; Trident/7.0; .NET4.0C; .NET4.0E)
State: {"ckey":"sulta","interface":"ShipSelect","window":{"key":"[0x210168c5]-main","size":null,"fancy":1,"locked":0}}

TypeError: Unable to get property 'indexOf' of undefined or null reference
at isStyleSheetLoaded (http://127.0.0.1:59191/tgui-window-1.html:259:7)
at node.onload (http://127.0.0.1:59191/tgui-window-1.html:346:9)
User Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.2; WOW64; Trident/7.0; .NET4.0C; .NET4.0E)
State: {"ckey":"sulta","interface":"ShipSelect","window":{"key":"[0x210168c5]-main","size":null,"fancy":1,"locked":0}}

Testmerges:

Reproduction:

I just joined the game on the latest stable byond version and it seems to have hated that.