code: public static String getPid(EvaluationCtx context) {
          EvaluationResult attribute
                  = context.getResourceAttribute(STRING_ATTRIBUTE,
                          Constants.OBJECT.PID.attributeId,
                                                 null);
          BagAttribute element = getAttributeFromEvaluationResult(attribute);
          if (element == null) {
              logger.debug("PolicyFinderModule:getPid exit on can't get pid on request callback");
              return null;
          }
  
          if (!(element.getType().equals(STRING_ATTRIBUTE))) {
              logger.debug("PolicyFinderModule:getPid exit on couldn't get pid from xacml request non-string returned");
              return null;
          }
  
          return (element.size() == 1) ? (String) element.getValue() : null;
      }
docs: get the pid from the context, or null if unable