private String readASCII(int utfLen) {
    final int startIdx = pos;
    int index = pos;
    final int limit = index + utfLen;
    for (; index < limit; index++) {
      if ((bytes[index] & 0xff) >= 128) {
        return null;
      }
    }
    pos = limit;
    @SuppressWarnings("deprecation")
    final String string = new String(bytes, 0, startIdx, utfLen);
    return string;
  }
If the utf encoded data is all ASCII then return
a String containing that data. Otherwise return null.
geode-serialization/src/main/java/org/apache/geode/internal/serialization/ByteArrayDataInput.java