Applying the official solution leads to errors

[barrio]

The following error is shown:
Task.kt:
Error(5, 32) Object is not abstract and does not implement abstract member public abstract fun equals(p0: Object!): Bolean defined in java.util.Comparator

There are also errors concerning Test.Kt. Unfortunately the error messages are not copyable so I omit them here.
OS Windows 10, Browsers Chrome 62 & Firefox 56.