Single dash passed as positional arg disappears

This is with yargs v16.0.1.

Sample code in test.js:

const yargs = require('yargs/yargs')
const {hideBin} = require('yargs/helpers');
const argv = yargs(hideBin(process.argv))
      .command('$0 <foo>', 'the default command', (yargs) => {
        yargs
          .positional('foo', {type: 'string', required: true})
      }, (argv) => {
        console.log(argv)
      })
      .argv

Test:

$ node test.js -
{ _: [], '$0': 'test.js', foo: '' }
$ node test.js a
{ _: [], '$0': 'test.js', foo: 'a' }

This is unfortunate, as using - as a filename to mean stdin or stdout is a common convention.

Start with the reproduction in test.js and run both node test.js - and node test.js a to confirm the differing positional values. Trace the yargs-parser handling of a lone dash, then add a regression test showing that - remains the positional foo value and verify the existing parser tests still pass.