inflateNext method Null safety

Implementation

List<int>? inflateNext() {
  _bitBuffer = 0;
  _bitBufferLen = 0;
  if (output is OutputStream) {
    output.clear();
  }
  if (!inputSet || input.isEOS) {
    return null;
  }

  try {
    if (input is InputStream) {
      var i = input as InputStream;
      _blockPos = i.offset;
    }
    _parseBlock();
    // If it didn't finish reading the block, it will have thrown an exception
    _blockPos = 0;
  } catch (e) {
    return null;
  }

  if (output is OutputStream) {
    return output.getBytes() as List<int>;
  }
  return null;
}