Powershell completions not working with empty help string.

[LucasLehmann]

I came across a problem with the uutils coreutils package where the powershell completions didnt work, uutils/coreutils#5933, and was directed here. I discovered this is because in the generated ps1 file the line [CompletionResuIt]::new('seq', 'seq', [CompletionResultType]::ParameterValue, '') exists, this line seems to cause the completions to fail and fall back on completing files, i also noticed this is not an issue and everything works as intended when adding something here, be it ' ' or anything else.
I dont know how this and i have never used clap so i dont know what to do to try to replicate it. But i can duplicate the issue in for example rustups completion by replacing it an empty string in one of the completion elements.

[tertsdiepraam]

Here's a minimal example as cargo script:

#!/usr/bin/env -S cargo +nightly -Zscript
```
[dependencies]
clap = "4.4.18"
clap_complete = "4.4.10"
```

use clap::Command;
use clap_complete::{generate, Shell::PowerShell};

fn main() {
    let mut cmd = Command::new("test").subcommand(Command::new("foo").about(""));
    generate(PowerShell, &mut cmd, "test", &mut std::io::stdout());
}

Upon further inspection, I do think we have to fix this in uutils as well, but I think clap_complete should be aware that an empty about breaks completion and fall back to something else.