title: Django model FileField is set to "null" instead of url to the file when using Google Cloud Storage
body: <p>I am running a File manager app on Local machine using Google Cloud Sql Proxy and storing the files in a Google Cloud Storage bucket.
  The file is being saved in the bucket, but the FileField is set to "null". I want it to show the url by which I can access the file.</p>
  
  <p>I am following this answer <a href="https://stackoverflow.com/questions/34247702/configure-django-and-google-cloud-storage/50116653#50116653">Configure Django and Google Cloud Storage?</a></p>
  
  <p>I have set the Google Cloud Storage bucket to public.</p>
  
  <p>Django Model:</p>
  
  <pre class="lang-py prettyprint-override"><code>class Document(models.Model):
      docfile = models.FileField(upload_to='documents/%Y/%m/%d')
  </code></pre>
  
  <p>Setting.py:</p>
  
  <pre class="lang-py prettyprint-override"><code>#MEDIA_URL = "/media/"
  #MEDIA_ROOT = os.path.join(BASE_DIR, 'media')
  
  DEFAULT_FILE_STORAGE = 'storages.backends.gcloud.GoogleCloudStorage'
  GS_BUCKET_NAME = 'printhub-files'
  
  GS_PROJECT_ID = 'preasy-53c43'
  GS_MEDIA_BUCKET_NAME = 'printhub-files'
  # GS_STATIC_BUCKET_NAME = '&lt;name-of-static-bucket&gt;'
  # STATIC_URL = 'https://storage.googleapis.com/{}/'.format(GS_STATIC_BUCKET_NAME)
  MEDIA_URL = 'https://storage.googleapis.com/{}/'.format(GS_MEDIA_BUCKET_NAME)
  </code></pre>
  
  <p>Expected Result:</p>
  
  <pre><code>{
      "id": 13,
      "docfile": "https://storage.googleapis.com/bucket/documents/2019/11/03/myfile.pdf",
  }
  </code></pre>
  
  <p>Actual Result:</p>
  
  <pre><code>{
      "id": 13,
      "docfile": null,
  }
  </code></pre>
  
  <p>If I change my Settings.py to (uncomment line 1,2. Comment line 4), the file is saved on my local machine media/ folder, and "docfile" is set to the bucket url:</p>
  
  <pre class="lang-py prettyprint-override"><code>MEDIA_URL = "/media/"
  MEDIA_ROOT = os.path.join(BASE_DIR, 'media')
  
  #DEFAULT_FILE_STORAGE = 'storages.backends.gcloud.GoogleCloudStorage'
  GS_BUCKET_NAME = 'printhub-files'
  
  GS_PROJECT_ID = 'preasy-53c43'
  GS_MEDIA_BUCKET_NAME = 'printhub-files'
  # GS_STATIC_BUCKET_NAME = '&lt;name-of-static-bucket&gt;'
  # STATIC_URL = 'https://storage.googleapis.com/{}/'.format(GS_STATIC_BUCKET_NAME)
  MEDIA_URL = 'https://storage.googleapis.com/{}/'.format(GS_MEDIA_BUCKET_NAME)
  </code></pre>
  
  <p>I get the output:</p>
  
  <pre><code>{
      "id": 13,
      "docfile": "https://storage.googleapis.com/bucket/documents/2019/11/03/myfile.pdf",
  }
  </code></pre>