How to use the @salesforce/command.flags.filepath function in @salesforce/command

export default class Dump extends SfdxCommand {

  public static description = messages.getMessage('commandDescription');

  public static get usage() {
    return SfdxCommand.usage.replace('<%= command.id %>', 'automig:dump');
  }

  public static examples = [
  '$ sfdx automig:dump --targetusername username@example.com --objects Opportunity,Case,Account:related,Task:related --outputdir ./dump',
  '$ sfdx automig:dump --targetusername username@example.com --config automig-dump-config.json'
  ];

  protected static flagsConfig = {
    // flag with a value (-n, --name=VALUE)
    config: flags.filepath({
      char: 'f',
      description: messages.getMessage('configFlagDescription')
    }),
    objects: flags.array({
      char: 'o',
      description: messages.getMessage('objectsFlagDescription'),
      map: (value: string) => {
        const [ object, target = 'query' ] = value.split(':');
        return { object, target };
      }
    }),
    outputdir: flags.directory({
      char: 'd',
      description: messages.getMessage('outputDirFlagDescription')
    }),
    excludebom: flags.boolean({