unix> curl -X POST --data @- --dump - http://localhost:8529/_api/document?collection=productsUnknown
{ "Hello": "World" }

HTTP/1.1 404 Not Found
content-type: application/json; charset=utf-8

{ 
  "error" : true, 
  "errorMessage" : "collection /_api/collection/productsUnknown not found", 
  "code" : 404, 
  "errorNum" : 1203 
}