docs: def _get_credentials(vcap_services, service_name=None):
      """Retrieves the credentials of the VCAP Service of the specified `service_name`.  If
      `service_name` is not specified, it takes the information from STREAMING_ANALYTICS_SERVICE_NAME environment
      variable.
  
      Args:
          vcap_services (dict): A dict representation of the VCAP Services information.
          service_name (str): One of the service name stored in `vcap_services`
  
      Returns:
          dict: A dict representation of the credentials.
  
      Raises:
          ValueError:  Cannot find `service_name` in `vcap_services`
      """
      service_name = service_name or os.environ.get('STREAMING_ANALYTICS_SERVICE_NAME', None)
      # Get the service corresponding to the SERVICE_NAME
      services = vcap_services['streaming-analytics']
      creds = None
      for service in services:
          if service['name'] == service_name:
              creds = service['credentials']
              break
  
      # If no corresponding service is found, error
      if creds is None:
          raise ValueError("Streaming Analytics service " + str(service_name) + " was not found in VCAP_SERVICES")
      return creds