title: What is the proper HTTP response code for request without mandatory fields
body: <p>Consider simple case where user is deleting a post. This is simple HTTP DELETE/POST request with one mandatory field, post_id.</p>
  
  <p>What should server do if post_id is not provided?</p>
  
  <p>Apparently, user should never encounter this behaviour, so let's be puristic.</p>
  
  <p>My first take would be 400 bad request, but spec says</p>
  
  <pre><code>The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.
  </code></pre>
  
  <p>and I'd say missing field is OK from syntax/http POV, it's application domain-specific semantic requirement.</p>
  
  <p>200 OK with explanations is bad, 500 feels weird as this is request problem.</p>
  
  <p>Thoughs?</p>