Code cleanup (#1461)

* Code cleanup

* Fix flux tests

* Fix checkstyle errors

* Fix compile error

feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/propertiesversion/PropertiesFeatureToggleVersion.java

@@ -42,7 +42,7 @@ import java.util.Properties;
  */
 public class PropertiesFeatureToggleVersion implements Service {
 
-  private boolean isEnhanced;
+  private final boolean isEnhanced;
 
   /**
    * Creates an instance of {@link PropertiesFeatureToggleVersion} using the passed {@link

feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/User.java

@@ -29,7 +29,7 @@ package com.iluwatar.featuretoggle.user;
  */
 public class User {
 
-  private String name;
+  private final String name;
 
   /**
    * Default Constructor setting the username.

feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/UserGroup.java

@@ -35,8 +35,8 @@ import java.util.List;
  */
 public class UserGroup {
 
-  private static List<User> freeGroup = new ArrayList<>();
-  private static List<User> paidGroup = new ArrayList<>();
+  private static final List<User> freeGroup = new ArrayList<>();
+  private static final List<User> paidGroup = new ArrayList<>();
 
 
   /**