There is currently no way to encode an empty object {}, as empty tables are
encoded as empty lists [].
With this patch, encode() will ignore table fields with the key json.null (which
doesn't make sense anyways). This allows adding a field with key json.null to
force encoding it as an object.
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
304eec2eba