Default value for `in` parameter

Hi,

Is this the  right place to ask dbus questions?

For example, there is a dbus config (is from
https://gjs.guide/guides/gio/dbus.html#high-level-proxies):
```xml
<method name="ComplexMethod">
    <arg type="b" direction="in" name="input"/>
    <arg type="u" direction="out" name="length"/>
</method>
```

Is it possible to set a default value to parameter `input` and mark it as
unrequired?

Just like in spring mvc, we can set a parameter `required=false` and set
`default` value too:
`@RequestParam(required = false, defaultValue = "default value") String
parameter`