$ ./jq --version
jq-1.6-159-gcff5336

$ ./jq -n --jsonargs '$ARGS' 123 'invalid json'
{
  "positional": [
    123,
Assertion failed: (0 && "Invalid value"), function jv_dump_term, file jv_print.c, line 221.
    [1]    9056 abort      ./jq -n --jsonargs '$ARGS' 123 'invalid json'

# for some reason this don't assert but the invalid JSON is null
$ ./jq -n --jsonargs '$ARGS.positional[0,1]' 123 'invalid json'
123
null