code: func (s SandboxService) Post(sums []string) (data SandboxPostResponse, err error) {
  	smap := make(map[string]interface{})
  	for _, hashstr := range sums {
  		smap[hashstr] = nil
  	}
  	sboxReq := SandboxRequest{Checksums: smap}
  
  	body, err := JSONReader(sboxReq)
  	if err != nil {
  		return
  	}
  
  	err = s.client.magicRequestDecoder("POST", "/sandboxes", body, &data)
  	return
  }
docs: // Post creates a new sandbox on the chef-server. Deviates from the Chef-server api in that it takes a []string of sums for the sandbox instead of the IMO rediculous hash of nulls that the API wants. We convert it to the right structure under the hood for the chef-server api.
  // http://docs.getchef.com/api_chef_server.html#id38