When using the the unknown sub-command, the client will execute the default command which can output the unexpected message.

The right behavior:

```
$ git-pr lis

error: unknown sub-command: lis

Available sub-commands are:
// Ignore the following output.
```

The wrong behavior:

```
$ git-pr lis 123

error: unexpected input: 123 // <-- here wrong
usage: git-pr [options] [<COMMAND>]
-h, --help Show help
--verbose Turn on verbose output
--debug Turn on debugging output
--version Print the version of this tool
```

The default sub-command is `git-pr help`, so when the client doesn't identify the sub-command `git-pr lis`, it will execute `git-pr help` and will pass `lis 123` as the argument to the `git-pr help` command. And the `git-pr help` can resolve only one argument, which is `lis` in this example, so it would output `error: unexpected input: 123`.