How to use the loopback4-authentication.AuthErrorKeys.ClientUserMissing function in loopback4-authentication

async loginWithClientUser(
    @requestBody() req: LoginRequest,
  ): Promise {
    if (!this.client || !this.user) {
      throw new HttpErrors.Unauthorized(AuthErrorKeys.ClientInvalid);
    } else if (!this.client.userIds || this.client.userIds.length === 0) {
      throw new HttpErrors.UnprocessableEntity(AuthErrorKeys.ClientUserMissing);
    } else if (!req.client_secret) {
      throw new HttpErrors.BadRequest(AuthErrorKeys.ClientSecretMissing);
    }
    try {
      const payload: ClientAuthCode = {
        clientId: this.client.clientId,
        user: this.user,
      };
      return await this.createJWT(payload, this.client);
    } catch (error) {
      throw new HttpErrors.InternalServerError(
        AuthErrorKeys.InvalidCredentials,
      );
    }
  }