Why am I getting a nullptr from my bag file?

edit

I am playing back a bagfile and I get a nullptr when I should be getting actual data.

Below is a screenshot of the bagfile being viewed from RQT. There is only one message called "decomposition/sectors" and I am certain that it should have data. Yet, when I am playing back the bag file in C++ code for a unit test, I get a nullptr for this particular item. Why am I getting this? The other messages will be properly read and instantiated, but not this one.

Here is a snippet of code which shows how I am reading this:

  void CoverageReporterTester::SendMessage(const rosbag::MessageInstance& bag_msg)
  {
    if (topic_name == avidbots_topics::decomposition_sectors)
    {
      message_stack::sector_array msg1 = *bag_msg.instantiate<message_stack::sector_array>();
      SendMessage(topic_name, msg1);
    }
  }

  /* Read bag file */
  rosbag::Bag bag_file;
  std::string bag_dir = ros::package::getPath("coverage_reporter") +
                          "/test/data/bag_files/coverage_reporter.bag";

  bag_file.open(bag_dir, rosbag::bagmode::Read);

  /* List of topics we are interested in */
  std::vector<std::string> topics;
  topics.push_back(topics::decomposition_sectors);

  topics.push_back(avidbots_topics::static_3d_costmap_topic);

  rosbag::View view(bag_file, rosbag::TopicQuery(topics));

  /* Loop through each message in the bag file which is associated with one of our topics listed above */
  foreach(rosbag::MessageInstance const bag_msg, view)
  {
    coverage_reporter.SendMessage(bag_msg);
  }