code: protected String readText(Postcard postcard, String path, boolean html, boolean filesystem, OptionalThing<Locale> receiverLocale,
              OptionalThing<Object> dynamicData) {
          if (dynamicData.isPresent()) {
              final OptionalThing<String> assisted = assistDynamicText(postcard, path, html, filesystem, receiverLocale, dynamicData.get());
              if (assisted.isPresent()) {
                  return assisted.get();
              }
          }
          final String cacheKey = generateCacheKey(path, filesystem, receiverLocale);
          final String cached = textCacheMap.get(cacheKey);
          if (cached != null) {
              return cached;
          }
          synchronized (this) {
              final String retried = textCacheMap.get(cacheKey);
              if (retried != null) {
                  return retried;
              }
              final String read = doReadText(postcard, path, filesystem, receiverLocale);
              if (read == null) { // just in case
                  String msg = "Not found the text from the path: " + path + ", filesystem=" + filesystem;
                  throw new SMailIllegalStateException(msg);
              }
              textCacheMap.put(cacheKey, read);
              return textCacheMap.get(cacheKey);
          }
      }
docs: =============