code: public static NinjaMode determineModeFromSystemPropertiesOrProdIfNotSet() {
          
          Optional<NinjaMode> ninjaModeOptional = determineModeFromSystemProperties();
          NinjaMode ninjaMode;
          
          if (!ninjaModeOptional.isPresent()) {
              ninjaMode = NinjaMode.prod;
          } else {
              ninjaMode = ninjaModeOptional.get();
          }
          
          logger.info("Ninja is running in mode {}", ninjaMode.toString());
          
          return ninjaMode;
          
      }
docs: returns NinjaMode.dev if no mode is set. Or the valid mode
  set via a System Property called "ninja.mode".
  
  E.g. under mvn you can use mvn ... -Dninja.mode=prod or so. Valid values
  for ninja.mode are "prod", "dev", "test".
  
  @return The valid mode set via a System Property called "ninja.mode"
  or NinjaMode.dev if it is not set.