docs: @Nullable
      public final String getStringContent(final long blobHandle, @NotNull final Transaction txn) throws IOException {
          String result;
          result = stringContentCache.tryKey(this, blobHandle);
          if (result == null) {
              final InputStream content = getContent(blobHandle, txn);
              if (content == null) {
                  logger.error("Blob string not found: " + getBlobLocation(blobHandle), new FileNotFoundException());
              }
              result = content == null ? null : UTFUtil.readUTF(content);
              if (result != null && result.length() <= config.getBlobStringsCacheMaxValueSize()) {
                  if (stringContentCache.getObject(this, blobHandle) == null) {
                      stringContentCache.cacheObject(this, blobHandle, result);
                  }
              }
          }
          return result;
      }