code: @SuppressWarnings("unchecked")
      private Map<String, Object> readCachedETags() {
          File cachedETagsFile = getCachedETagsFile();
          Map<String, Object> cachedETags;
          if (cachedETagsFile.exists()) {
              JsonSlurper slurper = new JsonSlurper();
              cachedETags = (Map<String, Object>)slurper.parse(cachedETagsFile, "UTF-8");
          } else {
              cachedETags = new LinkedHashMap<String, Object>();
          }
          return cachedETags;
      }
docs: Reads the {@link #cachedETagsFile}
  @return a map containing the parsed contents of the cached etags file
  or an empty map if the file does not exist yet