docs: private final void _writeNull() throws IOException
      {
          if ((_outputTail + 4) >= _outputEnd) {
              _flushBuffer();
          }
          int ptr = _outputTail;
          char[] buf = _outputBuffer;
          buf[ptr] = 'n';
          buf[++ptr] = 'u';
          buf[++ptr] = 'l';
          buf[++ptr] = 'l';
          _outputTail = ptr+1;
      }