Problem with Lab18 uaa-guard-proxy, can deploy but can't detect buildpack

Got problem deploying the uaa-guard-proxy app. The buildpack for this app was not detected correctly. So the app cannot be started.

$ cat /tmp/cf-uaa-guard-service-proxy-manifest.yml

---

applications:

  - name: uaa-guard-proxy

    command: proxy

    path: proxy

    memory: 128M

    env:

      GUARD_COOKIE_SECRET: very-secret

      GUARD_DEFAULT_CALLBACK_URL: http://uaa-guard-proxy.local.pcfdev.io/auth/cloudfoundry/callback

      GUARD_LOGIN_URL: https://uaa1.local.pcfdev.io

      GUARD_CLIENT_KEY: oauth_showcase_authorization_code

      GUARD_CLIENT_SECRET: secret

      #GOPACKAGENAME: github.com/cloudfoundry/go-buildpack

$ cf push uaa-guard-proxy -p /tmp/cf-uaa-guard-service-git/cf-uaa-guard-service -f /tmp/cf-uaa-guard-service-proxy-manifest.yml

Pushing from manifest to org pcfdev-org / space pcfdev-space as admin...

Using manifest file /tmp/cf-uaa-guard-service-proxy-manifest.yml

Getting app info...

Creating app with these attributes...

+ name:       uaa-guard-proxy

  path:       /tmp/cf-uaa-guard-service-git/cf-uaa-guard-service

+ command:    proxy

+ memory:     128M

  env:

+   GUARD_CLIENT_KEY

+   GUARD_CLIENT_SECRET

+   GUARD_COOKIE_SECRET

+   GUARD_DEFAULT_CALLBACK_URL

+   GUARD_LOGIN_URL

  routes:

+   uaa-guard-proxy.local.pcfdev.io

Creating app uaa-guard-proxy...

Mapping routes...

Comparing local files to remote cache...

Packaging files to upload...

Uploading files...

 9.31 KiB / 9.31 KiB [==============================================================================================================] 100.00% 1s

Waiting for API to complete processing files...

Staging app and tracing logs...

   Downloading go_buildpack_new...

   Downloading java_buildpack...

   Downloading ruby_buildpack...

   Downloading dotnet-core_buildpack...

   Downloading nodejs_buildpack...

   Downloaded go_buildpack_new

   Downloading go_buildpack...

   Downloaded java_buildpack

   Downloading python_buildpack...

   Downloaded ruby_buildpack

   Downloading php_buildpack...

   Downloaded dotnet-core_buildpack

   Downloading staticfile_buildpack...

   Downloaded staticfile_buildpack

   Downloading binary_buildpack...

   Downloaded php_buildpack

   Downloaded binary_buildpack

   Downloaded nodejs_buildpack

   Downloaded python_buildpack

   Downloaded go_buildpack

   Creating container

   Successfully created container

   Downloading app package...

   Downloaded app package (9.3K)

   Staging...

   None of the buildpacks detected a compatible application

   Exit status 222

   Staging failed: Exited with status 222

   Destroying container

   Successfully destroyed container

Error staging application: An app was not successfully detected by any available buildpack

TIP: Use 'cf buildpacks' to see a list of supported buildpacks.

FAILED