How to use the @accounts/common.validators.validateUsername function in @accounts/common

'Unrecognized options for create user request',
        {
          username: user && user.username,
          email: user && user.email,
        },
        400,
      );
    }

    // In case where password is an object we assume it was prevalidated and hashed
    if (!user.password ||
        (isString(user.password) && !validators.validatePassword(user.password))) {
      throw new AccountsError('Password is required');
    }

    if (!validators.validateUsername(user.username) && !validators.validateEmail(user.email)) {
      throw new AccountsError('Username or Email is required');
    }

    const hashAlgorithm = this.options.passwordHashAlgorithm;
    const password = (user.password && hashAlgorithm) ?
      hashPassword(user.password, hashAlgorithm) : user.password;
    const userToCreate = { ...user, password };
    try {
      const userId = await this.transport.createUser(userToCreate);
      const { onUserCreated } = this.options;
      if (callback && isFunction(callback)) {
        callback();
      }
      if (isFunction(onUserCreated)) {
        try {
          await onUserCreated({ id: userId });