- Uses length of shortest array, unless useLongestLength is true. If useLongestLength is true, but defaults is not specified, will use null to fill in.
- The use of null here is consistent with our parsing of array literals (e.g. [0, "$field"] will become [0, null] if 'field' does not exist).
- 'defaults' cannot be specified unless useLongestLength is true.
- If any input is null, will return null. $map returns null if its input is nullish.
- Will error if any input is not an array (and is not nullish).
- Will error if 'defaults' is specified without 'useLongestLength', or is not the same length as 'inputs'.