code: public static String readDefaultJsonVersionedFile(Path config, String version, String type) throws IOException {
          Path defaultConfigDir = config.resolve("_default");
          try {
              return readJsonVersionedFile(defaultConfigDir, version, type);
          } catch (NoSuchFileException e) {
              throw new IllegalArgumentException("Mapping file " + type + ".json does not exist for elasticsearch version " + version +
                      " in [" + defaultConfigDir + "] dir");
          }
      }
docs: Reads a mapping from config/_default/version/type.json file
  
  @param config Root dir where we can find the configuration (default to ~/.fscrawler)
  @param version Elasticsearch major version number (only major digit is kept so for 2.3.4 it will be 2)
  @param type The expected type (will be expanded to type.json)
  @return the mapping
  @throws IOException If the mapping can not be read