code: public boolean contains(final UTF8String substring) {
      if (substring.numBytes == 0) {
        return true;
      }
  
      byte first = substring.getByte(0);
      for (int i = 0; i <= numBytes - substring.numBytes; i++) {
        if (getByte(i) == first && matchAt(substring, i)) {
          return true;
        }
      }
      return false;
    }
docs: Returns whether this contains `substring` or not.