This matches the style in man(1) (except that we use the … ligature).
A previous iteration did the reverse (never use a space before the
ellipsis). That would be a smaller change.
Technically the equivalence would be something like
string length -q $str
test -n (string join \n -- $str | string collect)
To handle when str has multiple empty strings;
but quoting is easier to remember and enough for most practical purposes.