title: What HTTP error code for failure to create a new resource because a parent entity is gone
body: <p>Say i have an API exposing two related resources, Company which has many Employees.</p>
  
  <p>Say I create a new Company: POST <a href="http://domain/api/company/" rel="noreferrer">http://domain/api/company/</a> which returns something like <a href="http://domain/api/company/123" rel="noreferrer">http://domain/api/company/123</a>. </p>
  
  <p>If company/123 is removed from the system (say by a DELETE) then GET <a href="http://domain/api/company/123" rel="noreferrer">http://domain/api/company/123</a> could return HTTP response code 410 (Gone).</p>
  
  <p>My question is this. If I now try to create an Employee under Company/123 by doing POST <a href="http://domain/api/employees/" rel="noreferrer">http://domain/api/employees/</a> (with companyId set to 123 in the request body) what HTTP response code should be sent back by the server due to the invalid request? </p>
  
  <p>E.g. the request is correctly formated, but there is a logical error due to the fact that company 123 is gone.</p>
  
  <p>Internal Server Error 500?</p>