title: JSON in post request works in HttpRequester but not in python Requests
body: <p>I'm stuck in web scraping a page using Python. Basically, the following is the request from HttpRequester (in Mozilla) and it gives me the right response.</p>
  <pre><code>POST https://www.hpe.com/h20195/v2/Library.aspx/LoadMore
  Content-Type: application/json
  {&quot;sort&quot;: &quot;csdisplayorder&quot;, &quot;hdnOffset&quot;: &quot;1&quot;, &quot;uniqueRequestId&quot;: &quot;d6da6a30bdeb4d77b0e607a6b688de1e&quot;, &quot;test&quot;: &quot;&quot;, &quot;titleSearch&quot;: &quot;false&quot;, &quot;facets&quot;: &quot;wildcatsearchcategory#HPE,cshierarchycategory#No,csdocumenttype#41,csproducttype#18964&quot;}
   -- response --
  200 OK
  Cache-Control:  private, max-age=0
  Content-Length:  13701
  Content-Type:  application/json; charset=utf-8
  Server:  Microsoft-IIS/7.5
  X-AspNet-Version:  4.0.30319
  X-Powered-By:  ASP.NET
  Date:  Sat, 28 May 2016 04:12:57 GMT
  Connection:  keep-alive
  </code></pre>
  <p>The exact same operation in python 2.7.1 using Requests, fails with an error. The following is the code snippet:</p>
  <pre><code>jsonContent = {&quot;sort&quot;: &quot;csdisplayorder&quot;, &quot;hdnOffset&quot;: &quot;1&quot;, &quot;uniqueRequestId&quot;: &quot;d6da6a30bdeb4d77b0e607a6b688de1e&quot;, &quot;test&quot;: &quot;&quot;, &quot;titleSearch&quot;: &quot;false&quot;, &quot;facets&quot;: &quot;wildcatsearchcategory#HPE,cshierarchycategory#No,csdocumenttype#41,csproducttype#18964&quot;}
  
  catResponse = requests.post('https://www.hpe.com/h20195/v2/Library.aspx/LoadMore', json = jsonContent)
  </code></pre>
  <p>The following is the error that I get:</p>
  <pre><code>{&quot;Message&quot;:&quot;Value cannot be null.\r\nParameter name: source&quot;,&quot;StackTrace&quot;:&quot;   at
   System.Linq.Enumerable.Contains[TSource](IEnumerable`1 source, TSource value, I
  EqualityComparer`1 comparer)\r\n   
  </code></pre>
  <p>More information:
  The Post request that I'm looking for is fired upon:</p>
  <blockquote>
  <ol>
  <li><p>opening this web page: <a href="https://www.hpe.com/h20195/v2/Library.aspx?doctype=41&amp;doccompany=HPE&amp;footer=41&amp;filter_doctype=no&amp;filter_doclang=no&amp;country=&amp;filter_country=no&amp;cc=us&amp;lc=en&amp;status=A&amp;filter_status=rw#doctype-41&amp;doccompany-HPE&amp;prodtype_oid-18964&amp;status-a&amp;sortorder-csdisplayorder&amp;teasers-off&amp;isRetired-false&amp;isRHParentNode-false&amp;titleCheck-false" rel="nofollow noreferrer">https://www.hpe.com/h20195/v2/Library.aspx?doctype=41&amp;doccompany=HPE&amp;footer=41&amp;filter_doctype=no&amp;filter_doclang=no&amp;country=&amp;filter_country=no&amp;cc=us&amp;lc=en&amp;status=A&amp;filter_status=rw#doctype-41&amp;doccompany-HPE&amp;prodtype_oid-18964&amp;status-a&amp;sortorder-csdisplayorder&amp;teasers-off&amp;isRetired-false&amp;isRHParentNode-false&amp;titleCheck-false</a></p>
  </li>
  <li><p>Clicking on the &quot;Load more&quot; grey button at the end of the page</p>
  </li>
  </ol>
  </blockquote>
  <p>I'm capturing the exact set of request headers and response from the browser operation and trying to mimic that in Postman, Python code and HttpRequester (Mozilla).</p>
  <p>It flags the same error (mentioned above) with Postman and Python, but works with no headers set on my part with HttpRequester.</p>
  <p>Can anyone think of an explanation for this?</p>