Yoichi Nakayama <yoichi.nakayama@gmail.com> writes:
> When json-pretty-print applied to "{}", it is
> unexpectedly converted to "null".
> This is caused by internal representations of null
> and empty object are the same:
>   (json-read-from-string "{}") ; => nil
>   (json-read-from-string "null") ; => nil

please find a patch attached. This patch uses :json-null to distinguish,
during pretty-print, between the value null and an empty object.

All tests pass and many new tests are added.

Best