[11.x] Fix prompting for missing array arguments on artisan command

[macocci7]

This PR fixes the bug below:

When an Artisan Command has array arguments configuration, like:

protected $signature = 'app:foo {args*}';

promptForMissingArgumentsUsing() doesn't work,

because $input->getArgument($argument->getName()) returns empty array, and judgement in promptForMissingArguments() method of Illuminate\Console\Concerns\PromptsForMissingInput uses is_null(), which should be replaced with empty() .
empty() method also covers string argument, like:

protected $signature = 'app:foo {arg}';

[taylorotwell]

I'm leaving in draft until @jessarcher reviews it.

[macocci7]

I understand.

[macocci7]

OK.That's right.
Thank you for your suggestion.

[taylorotwell]

Personally I think this needs more thought. If you provide the argument on the CLI, you would get the argument as an array using $this->argument. With this, the argument would be a string. That feels inconsistent.

[jessarcher]

Personally I think this needs more thought. If you provide the argument on the CLI, you would get the argument as an array using $this->argument. With this, the argument would be a string. That feels inconsistent.

Good catch. I've updated it to wrap the response in an array. There isn't a good prompt for entering multiple arbitrary values, so with the default behaviour, you'd always get an array of one item.

It's possible for someone to provide their own prompt callback that can return multiple values using whatever implementation they like (multiselect of known options, multisearch against the DB, text prompts in a loop that continues until an empty response, or some sort of space/comma/newline separated answer).

[taylorotwell]

Thanks!