parameter and subcommand confusion

[binabik]

Hi,

I have a small application which reads a file, this is specified as in the main @Command class:

    @Parameters(
            paramLabel = "FILE",
            arity = "1",
            description = {
                    "Excel input file"
            },
            scope = ScopeType.LOCAL
    )
    private File xls;

The application also has a subcommand, called validate, which doesn't require that parameter, but takes a list of Files instead. However, when trying to execute the validate subcommand, i get the following error:

user@host:~ $ generator validate generated.xml

Missing required parameter: 'FILE'
Usage: generator [-dfhV] [-k=<keySize>] FILE [COMMAND]

Does a Thing with the Excel file.

      FILE        Excel input file
  -d, --debug     Show debugging output.
                    Default: false
  -f, --force     Overwrite existing output.
                    Default: false
  -h, --help      Show this help message and exit.
  -k, --keylength=<keySize>
                  Set generated dictionary key length.
                    Default: 4
  -V, --version   Print version information and exit.
Commands:
  help      Displays help information about the specified command
  validate  Validate VDF schemas.

I can call the help subcommand on validate:

user@host:~ $ generator help validate                          

Usage: vdf-generator validate [-hV] SCHEMA...
Validates some XML files.
      SCHEMA...   An XML file, or a directory containing a number of XML files.
  -h, --help      Show this help message and exit.
  -V, --version   Print version information and exit.

But trying to call the help mixin via -h returns the main usage message:

generator validate -h  

Missing required parameter: 'FILE'
Usage: vdf-generator [-dfhV] [-k=<keySize>] FILE [COMMAND]
# SNIP SNIPPETY SNIP

It seems either me or picocli is doing something wrong (I'm assuming it's me). Any suggestions?

(By making the FILE parameter arity "0..1" and manually validating whether it's been passed to the main command, I can get it to work. That doesn't quite feel like it's correct though.)