When the merge phase combines Str patterns, if either is undefined or unequal lengths are found, we just ditch the entire pattern. This could be more refined, e.g.zip_longest and mark the suffix regex-optional, although that begs the question what to do about combining optional suffixes, or if such a thing is even valid. Still, there's almost certainly room for some improvement here.
When the merge phase combines Str patterns, if either is undefined or unequal lengths are found, we just ditch the entire pattern. This could be more refined, e.g.
zip_longestand mark the suffix regex-optional, although that begs the question what to do about combining optional suffixes, or if such a thing is even valid. Still, there's almost certainly room for some improvement here.