psl::suffix_str(".") returning Some("") might be inconsistent with the official PSL algorithm

[Scripter17]

The very informal "formal" PSL algorithm specifies that labels cannot be empty.

Currently, psl::suffix_str(".") and psl::suffix_str("..") return Some(""), which seems to be be in violation of that rule?

Interestngly, while psl::domain_str("com..") returns Some("com.") (consistent with the above), psl::domain_str("..") returns None, which seems like the "labels cannot be empty" rule is observed for the not suffix part of a registerable domain.