title: Google App Engine showing a lot of 204 and I can't get any log
body: <p>I'm using google app engine with Python
  A lot of my users are getting return code 204 (I can see on the Stackdriver log)</p>
  
  <p>It's the same page (that returns a json that comes from datastore) and for some reason sometimes it's returning 204 (no Content) even thought there are valid contents.</p>
  
  <p>I have try...catches on my get method and they are never triggered.
  I have logging lines like: logging.info(u'right in the begging of method') 
  and they aren't printed when the return code is 204.</p>
  
  <p>I get this kind of entry on the log viewer:</p>
  
  <blockquote>
    <p>179.236.114.131 - - [04/Jan/2017:03:26:50 +0000] "GET /querywg?date=2017-01-04&amp;categoria=filme&amp;app_type=free HTTP/1.1" 204
    117847 - "okhttp/3.4.1" "gtvbrapp.guiatvbr.com.br" ms=19 cpu_ms=0
    cpm_usd=0.000013170428 loading_request=0 instance=-
    app_engine_release=1.9.48 trace_id=4c71730e72178c723437b2f196f44166</p>
  </blockquote>
  
  <p>All of them have the <code>instance=-</code> instead of a long number.</p>
  
  <p>Any ideas?</p>
  
  <p>The get() method (and dependencies):</p>
  
  <pre><code>def getAllOperadoras(self):
  
    ret = []
    operadoras_query = OperadorasList.query().order(-OperadorasList.lastupdate).fetch(1)
  
    for ops in operadoras_query:
        return ops.listaOperadoras
  
    return '[]'
  
    def getOperadora(self, id):
  
      operadora = Operadoras.get_by_id(id)
  
      if(operadora):
          return operadora.canaisJson
  
      return '[]'
  
  
   def get(self):
  
      idOperadora = self.request.get('id')
  
      ret = ''
      if(idOperadora):
          ret = self.getOperadora(idOperadora)
      else:
          ret = self.getAllOperadoras()
  
      self.response.headers['Cache-Control'] = "public, max-age=%d" % constants.CACHE_CONTROL_SIZE
      self.response.headers['Content-Type'] = 'application/json; charset=utf-8'
      self.response.out.write(ret)
  </code></pre>
  
  <p>the app.yaml:</p>
  
  <pre><code>application: some-invented-id
  version: 7
  runtime: python27
  api_version: 1
  instance_class: F2
  threadsafe: true
  
  env_variables:
  
  handlers:
  - url: /images
    static_dir: images
  
  - url: /css
    static_dir: css
  
  - url: /js
    static_dir: js
  
  - url: /font
    static_dir: font
  
  - url: /data
    static_dir: data
    mime_type: application/json
  
  # Endpoints handler
  - url: /_ah/spi/.*
    script: services.APPLICATION
  
  - url: /robots.txt
    static_files: 1
    upload: robots.txt
  
  - url: /.*
    script: mainpage.app
    secure: optional
  
  builtins:
  - deferred: on
  - appstats: on
  - remote_api: on
  
  libraries:
  - name: webapp2
    version: latest
  - name: jinja2
    version: latest
  - name: pycrypto
    version: latest
  - name: endpoints
    version: 1.0
  </code></pre>