`String.words` of a string with no words in it returns a 1-member Array instead of an empty Array

Found against: gren 0.6.6, gren-lang/core 7.4.2, node 22

Summary

String.words's docs say this:

Break a string into words, splitting on chunks of whitespace.

When the string it parses has 2 words, the resulting Array has 2 items.
When the string has 1 word, it returns an Array of 1 item, regardless of whitespace before or after.

Array.length (String.words "a b")   -- 2
Array.length (String.words " a ")   -- 1, the padding dropped

However when the input has no words, the result is not an empty Array.
Instead it is an Array of one empty string.

Array.length (String.words "")      -- 1
Array.first  (String.words "")      -- Just ""

The reason I believe this is a defect rather than a choice is that words never returns
empty strings anywhere else. " a " does not answer [ "", "a", "" ]; a run of
whitespace between two words does not return empty strings between them.

Every caller can therefore assume that a word is a non-empty string.

Looking at it another way, it's odd that the length of words "a" is the same length of words ""

> String.words "a b c"
["a", "b", "c"] : Array String

> String.words "a b"
["a", "b"] : Array String

> String.words "a"
["a"] : Array String

> String.words ""
[""] : Array String

Start at the String.words entry point and compare its behavior for empty, whitespace-only, one-word, and multi-word strings. Add coverage showing that an input with no words produces an empty Array, and confirm the existing examples with one or more words remain unchanged.