addFile method Null safety

Implementation

void addFile(ArchiveFile file) {
  final fileData = _ZipFileData();
  _data.files.add(fileData);

  fileData.name = file.name;
  fileData.time = _data.time;
  fileData.date = _data.date;
  fileData.mode = file.mode;
  fileData.isFile = file.isFile;

  InputStreamBase? compressedData;
  int crc32;

  // If the user want's to store the file without compressing it,
  // make sure it's decompressed.
  if (!file.compress) {
    if (file.isCompressed) {
      file.decompress();
    }

    compressedData = (file.content is InputStreamBase)
        ? file.content as InputStreamBase
        : InputStream(file.content);

    if (file.crc32 != null) {
      crc32 = file.crc32!;
    } else {
      crc32 = getFileCrc32(file);
    }
  } else if (file.isCompressed &&
      file.compressionType == ArchiveFile.DEFLATE) {
    // If the file is already compressed, no sense in uncompressing it and
    // compressing it again, just pass along the already compressed data.
    compressedData = file.rawContent;

    if (file.crc32 != null) {
      crc32 = file.crc32!;
    } else {
      crc32 = getFileCrc32(file);
    }
  } else {
    // Otherwise we need to compress it now.
    crc32 = getFileCrc32(file);

    dynamic bytes = file.content;
    if (bytes is InputStreamBase) {
      bytes = bytes.toUint8List();
    }
    bytes = Deflate(bytes as List<int>, level: _data.level).getBytes();
    compressedData = InputStream(bytes);
  }

  var filename = Utf8Encoder().convert(file.name);
  var comment =
      file.comment != null ? Utf8Encoder().convert(file.comment!) : null;

  _data.localFileSize += 30 + filename.length + compressedData!.length;

  _data.centralDirectorySize +=
      46 + filename.length + (comment != null ? comment.length : 0);

  fileData.crc32 = crc32;
  fileData.compressedSize = compressedData.length;
  fileData.compressedData = compressedData;
  fileData.uncompressedSize = file.size;
  fileData.compress = file.compress;
  fileData.comment = file.comment;
  fileData.position = _output!.length;

  _writeFile(fileData, _output!);

  fileData.compressedData = null;
}