jsonGetKeyList ( "" ) = "?"

[dansmith65]

It should either return an empty string, or an error (I'm not sure which, yet). It seems like it's trying to process it and reaching FM's recursion limits.

[jbante]

I favor the empty string result, unless an empty string does not count as well-formed JSON. An empty string does accurately describe the list of JSON keys in an empty string. But if an empty string isn't valid JSON, that perhaps merits some notification.