upload function Null safety

Implementation

void upload(SMHTaskInfo info, SendPort sendPort) {
  SMHApiTransferApis().uploadTask(
      info.libraryId,
      info.spaceId,
      info.userId,
      info.body,
      info.filePath,
      info.length,
      (result, error) {
        sendPort.send({'code': 'finish', 'result': result, 'error': error});
      },
      userToken: info.userToken,
      orgId: info.orgId,
      slice: info.slice,
      enableVerification: info.enableVerification,
      confirmKey: info.confirmKey,
      cancelToken: info.cancelToken,
      confirmKeyCalBack: (confirmKey) {
        sendPort.send({
          'code': 'confirmKey',
          'result': confirmKey,
          'error': null,
        });
      },
      conflictResolutionStrategy: info.conflictResolutionStrategy,
      onSendProgress: (int count, int total) {
        sendPort.send({
          'code': 'processing',
          'result': {'count': count, 'total': total},
          'error': null
        });
      });
}