title: The 'Access-Control-Allow-Origin' header contains the invalid value 'null'
body: <p>I have a Symfony2 application which I am trying to set up using the Nelmio CORS bundle. I am running this on an apache server (BitNami mampstack). </p>
  
  <p>No matter what I do, I keep getting this error logged to my browser's console:</p>
  
  <pre><code>XMLHttpRequest cannot load http://localhost:8000/avrequests. Response to preflight request doesn't pass access control check: The 'Access-Control-Allow-Origin' header contains the invalid value 'null'. Origin 'http://localhost:8080' is therefore not allowed access.
  </code></pre>
  
  <p>Sure enough my response headers read like this:</p>
  
  <pre><code>Access-Control-Allow-Origin:null
  Cache-Control:no-cache
  Connection:close
  Content-Type:text/html; charset=UTF-8
  Date:Sun, 29 Nov 2015 05:14:13 GMT
  Host:localhost:8000
  X-Debug-Token:3f40a5
  X-Debug-Token-Link:/_profiler/3f40a5
  X-Powered-By:PHP/5.5.27
  </code></pre>
  
  <p>This is the Nelmio configuration in my config.yml file (it's basically default values):</p>
  
  <pre><code>nelmio_cors:
      defaults:
          allow_credentials: false
          allow_origin: []
          allow_headers: []
          allow_methods: []
          expose_headers: []
          max_age: 0
          hosts: []
          origin_regex: false
      paths:
          '^/':
              allow_origin: ['*']
              allow_headers: ['origin', 'content-type']
              allow_methods: ['POST', 'PUT', 'GET', 'DELETE','OPTIONS']
              max_age: 3600
  </code></pre>
  
  <p>I have tried everything from adding this line into the httpd.conf file....</p>
  
  <pre><code>Header set Access-Control-Allow-Origin "*"
  </code></pre>
  
  <p>...to creating an .htaccess file. The bundle is properly included in my AppKernel.php file within Symfony. Nothing works; I cannot get anything to properly set the Access-Control-Allow-Origin header.</p>