How to determine if there is an error condition returned from RTC work item Reportable REST API?

We are using the following:

   Authenticate: https://localhost:9443/jts/authenticated/j_security_check?j_username=<username>&j_password=<password>

   Retrieve data: ...server:port/ccm/rpt/repository/workitem?fields=workitem/workItem...

1. How is it determined if there is a non-successful condition encountered with either of these? 
2. How is a successful return determined? 
3. How would one determine the difference between no data found and some kind of error condition?

   The following do not seem to shed any light on return or error codes, etc.:

• https://jazz.net/wiki/bin/view/Main/ReportsRESTAPI#workItem_type_com_ibm_team_worki
• http://open-services.net/pub/Main/ReportingHome/Reportable_Rest_Services_Interfaces-OSLC_Submission.pdf