Multiple types including Boolean

[ryym]

Hi,

I run into an issue about an option of multiple types including Boolean.
When a command has an Boolean option, we can use it without values.

{
  options: [{
    option: 'foo',
    type: 'Boolean'
  }]
}

command
# => { _: [] }

command --foo true
# => { _: [], foo: true }

command --foo  ## no values
# => { _: [], foo: true }

But when the option has other types in addition to Boolean, we can't so.

{
  options: [{
    option: 'foo',
    type: 'Boolean | String'
  }]
}

command
# => { _: [] }

command --foo value
# => { _: [], foo: 'value' }

command --foo true
# => { _: [], foo: true }

command --foo
# => { _: [] }
## Expected: { _: [], foo: true }

Is it possible to use the option as a flag when values are omitted even if it has multiple types?

Thanks.