#### Before this patch:

```console
$ bin/mruby -e '{}.key?'
trace (most recent call last):
-e:1: wrong number of arguments (ArgumentError)
```

#### After this patch:

```console
$ bin/mruby -e '{}.key?'
trace (most recent call last):
-e:1: wrong number of arguments (given 0, expected 1) (ArgumentError)
```