8079470: Misleading error message when explicit signature constructor is called with wrong arguments
Reviewed-by: jlaskey, hannesw
SyntaxError: Invalid JSON: <json>:1:12 Trailing comma is not allowed in JSON
{ "a": 333, }
^
SyntaxError: Invalid JSON: <json>:1:8 Trailing comma is not allowed in JSON
[ 4343, ]
^