writeInputStream method Null safety

Implementation

@override
void writeInputStream(InputStreamBase stream) {
  if (stream is InputStream) {
    final len = stream.length;

    if (_bufferPosition + len >= _buffer.length) {
      flush();

      if (_bufferPosition + len < _buffer.length) {
        for (int i = 0, j = _bufferPosition, k = stream.offset; i < len;
             ++i, ++j, ++k) {
          _buffer[j] = stream.buffer[k];
        }
        _bufferPosition += len;
        _length += len;
        return;
      }
    }

    if (_bufferPosition > 0) {
      flush();
    }
    _fp.writeFromSync(stream.buffer, stream.offset, stream.offset + stream.length);
    _length += stream.length;
  } else {
    var bytes = stream.toUint8List();
    writeBytes(bytes);
  }
}