processItem method Null safety

Implementation

processItem(PipelineFlowItem? item) async {
  String? next = start;
  // Process each connection
  for (var connection in connections) {
    String? step = processes.nameFor(connection.source);
    // check if the steps are connected
    if (step != null && step == next) {
      final operation = registry.operationFor(step);
      if (operation != null && item != null) {
        item = await operation.process(item);
        if (item == null) break;
      }
      next = processes.nameFor(connection.target);
    } else {
      throw Exception(
        'Pipeline Exception: Next step ($next) does not match '
        'the current step ($step)',
      );
    }
  }

  /// Emit result only if pipeline completed with a non-null item with data
  if (item != null) {
    result(item);
  }
}