code: private HashMap<SecretKey, SecureContainer> retrieveContainers() {
          HashMap<SecretKey, SecureContainer> containers = null;
          String workingDir = getMain().getFileSystemManager().getSystemDataLocation().getAbsolutePath();
          final String containerFile = workingDir + File.separator
                  + "containers.ser";
          try {
              FileInputStream fileIn = new FileInputStream(containerFile);
              ObjectInputStream in = new ObjectInputStream(fileIn);
              Object o = in.readObject();
              if (o instanceof HashMap) {
                  containers = (HashMap) o;
              }
              in.close();
              fileIn.close();
          } catch (FileNotFoundException e) {
              return null;
          } catch(IOException | ClassNotFoundException e) {
              logger.error("Unable to retrieve containers from file", e);
          }
  
          return containers;
      }
docs: Retrieves the containers from ./system/data/containers.ser if the file is found, else returns null
  
  @return the containers from ./system/data/containers.ser if the file is found, else null