Using BooleanOptionalAction and ArgumentDefaultsHelpFormatter results in repeating the default argument twice in the help ouput

[pes10k]

// example.js
const argparseLib = require('argparse')

const parser = new argparseLib.ArgumentParser({
  formatter_class: argparseLib.ArgumentDefaultsHelpFormatter
})
parser.add_argument('-e', '--an-example', {
  help: 'An example flag.',
  action: argparseLib.BooleanOptionalAction,
  default: true
})
const args = parser.parse_args()

$ node example.js --help
usage: example.js [-h] [-e | --an-example | --no-an-example]

optional arguments:
  -h, --help            show this help message and exit
  -e, --an-example, --no-an-example
                        An example flag. (default: true) (default: true)

The issue is that (default: true) is repeated (e.g. (default: true) (default: true))