[ljm]

I'm not sure it's any more general considering that you have to return an array and also treat an empty array as a 'null' value.

Or to put it another way, if I reviewed code where someone used flatMap for anything other than lists of lists I'd be likely to suggest filter/map or reduce or some other convenient equivalent depending on the purpose of the code.

Something like Ruby's filter_map[0] would do the job, although not with this particular example (because 0 is truthy in Ruby).

[0] https://ruby-doc.org/core-3.1.0/Enumerable.html#method-i-fil...