code: public List<ConfigMessage> init(Processor processor) {
          List<ConfigMessage> configMessages = new ArrayList<>();
  
          if (action.getPredicate() != null) {
              try {
                  predicate = ExpressionHandlerFactory.getHandler(action.getPredicate());
  
                  predicate.init(processor, getAction(), true);
  
                  if (!isUsesHeaders()) {
                      setUsesHeaders(predicate.isUsesHeaders());
                  }
                  if (!isUsesContent()) {
                      setUsesContent(predicate.isUsesContent());
                  }
  
              } catch (Throwable t) {
                  log.severe("Failed to initialise predicate for action:" + action, t);
                  ConfigMessage configMessage = new ConfigMessage();
                  configMessage.setSeverity(Severity.Error);
                  configMessage.setMessage(t.getMessage());
                  configMessage.setProcessor(processor.getDescription());
                  configMessage.setAction(action.getDescription());
                  configMessages.add(configMessage);
              }
          }
  
          return configMessages;
      }
docs: This method initialises the process action handler.
  
  @param processor The processor