SettingSource
TestSceneModSettings
As they're not really testing anything visual.
TestCustomisableModRuleset
DifficultyCalculator
IWorkingBeatmap
BeatmapDifficulty.ID
CheckCompatibleSet
As it turns out, C# 8 provides an attribute that allows annotating that an `out` parameter's nullability depends on the method's return value, which is exactly what is desired here.