Code cleanup (#1461)

* Code cleanup

* Fix flux tests

* Fix checkstyle errors

* Fix compile error

extension-objects/src/main/java/concreteextensions/Commander.java

@@ -35,7 +35,7 @@ public class Commander implements CommanderExtension {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Commander.class);
 
-  private CommanderUnit unit;
+  private final CommanderUnit unit;
 
   public Commander(CommanderUnit commanderUnit) {
     this.unit = commanderUnit;

extension-objects/src/main/java/concreteextensions/Sergeant.java

@@ -35,7 +35,7 @@ public class Sergeant implements SergeantExtension {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Sergeant.class);
 
-  private SergeantUnit unit;
+  private final SergeantUnit unit;
 
   public Sergeant(SergeantUnit sergeantUnit) {
     this.unit = sergeantUnit;

extension-objects/src/main/java/concreteextensions/Soldier.java

@@ -34,7 +34,7 @@ import units.SoldierUnit;
 public class Soldier implements SoldierExtension {
   private static final Logger LOGGER = LoggerFactory.getLogger(Soldier.class);
 
-  private SoldierUnit unit;
+  private final SoldierUnit unit;
 
   public Soldier(SoldierUnit soldierUnit) {
     this.unit = soldierUnit;