For some reason, or possibly just through my carelessness and for no
real reason, json_object() currently disallows empty strings as object
keys. However silly empty string keys might be, they are apparently
allowed by the JSON rfcs, and this behaviour by json_object() is
inconsistent with what the json parser and other json generating
functions allow, so I propose to remove the restriction, unless I hear
any objections.
cheers
andrew