docs: public String readUTF8(int index, final char[] buf) {
          int item = readUnsignedShort(index);
          if (index == 0 || item == 0) {
              return null;
          }
          String s = strings[item];
          if (s != null) {
              return s;
          }
          index = items[item];
          strings[item] = readUTF(index + 2, readUnsignedShort(index), buf);
          return strings[item];
      }