From type/IO/Path

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method z(IO::Path:D: --> Bool:D)

Returns True if the invocant is a path that exists and has size of 0. May be called on paths that are directories, in which case the reported file size (and thus the result of this method) is dependent on the operating system. The method will fail with X::IO::DoesNotExist if the path points to a non-existent filesystem entity.