code: public static AlluxioConfiguration merge(AlluxioConfiguration conf, Map<?, ?> properties,
        Source source) {
      AlluxioProperties props = conf.copyProperties();
      props.merge(properties, source);
      return new InstancedConfiguration(props);
    }
docs: Merges the current configuration properties with new properties. If a property exists
  both in the new and current configuration, the one from the new configuration wins if
  its priority is higher or equal than the existing one.
  
  @param conf the base configuration
  @param properties the source {@link Properties} to be merged
  @param source the source of the the properties (e.g., system property, default and etc)
  @return a new configuration representing the merged properties