Hotfix route generation for null beatmapset on event.
Hotfix route generation for null beatmapset on event.

Laravel 6 route doesn't allow null value if the route parameter is required, but is fine with it if
the parameter is keyed with the parameter name; then it generates the
same route as 5.5 did.

notbakaneko/osu-web,nekodex/osu-web,LiquidPL/osu-web,nanaya/osu-web,LiquidPL/osu-web,nanaya/osu-web,notbakaneko/osu-web,ppy/osu-web,ppy/osu-web,nanaya/osu-web,nanaya/osu-web,ppy/osu-web,ppy/osu-web,omkelderman/osu-web,LiquidPL/osu-web,nekodex/osu-web,notbakaneko/osu-web,omkelderman/osu-web,omkelderman/osu-web,nekodex/osu-web,nanaya/osu-web,nekodex/osu-web,omkelderman/osu-web,nekodex/osu-web,ppy/osu-web,notbakaneko/osu-web,notbakaneko/osu-web,LiquidPL/osu-web,LiquidPL/osu-web