Functional interfaces should be annotated as functional interfaces

Mage.Client/src/main/java/mage/client/util/Command.java

@@ -3,7 +3,7 @@ package mage.client.util;
 /**
  * @author nantuko
  */
+@FunctionalInterface
 public interface Command {
-
     void execute();
 }

Mage.Client/src/main/java/mage/client/util/Listener.java

@@ -34,6 +34,7 @@ import java.io.Serializable;
  * @author BetaSteward_at_googlemail.com
  * @param <E>
  */
+@FunctionalInterface
 public interface Listener<E extends Event> extends Serializable {
 
     void event(E event);

Mage.Client/src/main/java/org/mage/card/arcane/TextboxRule.java

@@ -23,6 +23,7 @@ public class TextboxRule {
 
     // An attributed region in the text, which can be applied to an
     // attributed string.
+    @FunctionalInterface
     public interface AttributeRegion {
 
         void applyToAttributedString(AttributedString str, Font normal, Font italic);

Mage.Server.Plugins/Mage.Game.CanadianHighlanderDuel/target/maven-archiver/pom.properties

@@ -1,5 +1,5 @@
 #Generated by Maven
-#Sun Feb 05 18:32:22 AEDT 2017
+#Wed Feb 15 19:18:14 MSK 2017
 version=1.4.21
 groupId=org.mage
 artifactId=mage-game-canadianhighlanderduel

Mage.Server/src/main/java/mage/server/SessionManager.java

@@ -37,6 +37,8 @@ import mage.players.net.UserData;
 import org.apache.log4j.Logger;
 import org.jboss.remoting.callback.InvokerCallbackHandler;
 
+import javax.annotation.Nonnull;
+
 /**
  * @author BetaSteward_at_googlemail.com
  */
@@ -51,10 +53,7 @@ public class SessionManager {
 
     private final ConcurrentHashMap<String, Session> sessions = new ConcurrentHashMap<>();
 
-    public Session getSession(String sessionId) {
+    public Session getSession(@Nonnull String sessionId) {
-        if (sessionId == null) {
-            return null;
-        }
         Session session = sessions.get(sessionId);
         if (session != null && session.getUserId() != null && UserManager.getInstance().getUser(session.getUserId()) == null) {
             logger.error("User for session " + sessionId + " with userId " + session.getUserId() + " is missing. Session removed.");
@@ -209,11 +208,11 @@ public class SessionManager {
         return false;
     }
 
-    public boolean isValidSession(String sessionId) {
+    public boolean isValidSession(@Nonnull String sessionId) {
         return sessions.containsKey(sessionId);
     }
 
-    public Optional<User> getUser(String sessionId) {
+    public Optional<User> getUser(@Nonnull String sessionId) {
         Session session = sessions.get(sessionId);
         if (session != null) {
             return UserManager.getInstance().getUser(sessions.get(sessionId).getUserId());

Mage.Server/src/main/java/mage/server/game/GameCallback.java

@@ -34,6 +34,7 @@ import mage.MageException;
  *
  * @author BetaSteward_at_googlemail.com
  */
+@FunctionalInterface
 public interface GameCallback {
 
     void gameResult(String result) throws MageException;

Mage.Server/src/main/java/mage/server/game/GameController.java

@@ -978,8 +978,8 @@ public class GameController implements GameCallback {
         }
     }
 
+    @FunctionalInterface
     interface Command {
-
         void execute(UUID player);
     }
 

Mage.Server/src/main/java/mage/server/services/FeedbackService.java

@@ -5,6 +5,7 @@ package mage.server.services;
  *
  * @author noxx
  */
+@FunctionalInterface
 public interface FeedbackService {
 
     /**

Mage.Server/src/main/java/mage/server/services/LogService.java

@@ -5,6 +5,7 @@ package mage.server.services;
  *
  * @author noxx
  */
+@FunctionalInterface
 public interface LogService {
 
     /**

Mage/src/main/java/mage/MageItem.java

@@ -35,6 +35,7 @@ import java.util.UUID;
  *
  * @author BetaSteward_at_googlemail.com
  */
+@FunctionalInterface
 public interface MageItem extends Serializable {
 
     UUID getId();

Mage/src/main/java/mage/abilities/condition/Condition.java

@@ -10,6 +10,7 @@ import mage.game.Game;
  *
  * @author nantuko, noxx
  */
+@FunctionalInterface
 public interface Condition extends Serializable {
 
     public enum ComparisonType {

Mage/src/main/java/mage/abilities/costs/AdjustingSourceCosts.java

@@ -1,3 +1,4 @@
+/*
 /*
  *  Copyright 2010 BetaSteward_at_googlemail.com. All rights reserved.
  *
@@ -38,6 +39,7 @@ import mage.game.Game;
  *
  * @author nantuko
  */
+@FunctionalInterface
 public interface AdjustingSourceCosts {
     void adjustCosts(Ability ability, Game game);
 }

Mage/src/main/java/mage/abilities/costs/mana/AlternateManaPaymentAbility.java

@@ -38,6 +38,7 @@ import mage.game.Game;
  *
  * @author LevelX2
  */
+@FunctionalInterface
 public interface AlternateManaPaymentAbility {
     /**
      * Adds the special action to the state, that allows the user to do the alternate mana payment

Mage/src/main/java/mage/abilities/mana/builder/Builder.java

@@ -32,6 +32,7 @@ import java.io.Serializable;
 /**
  * @author noxx
  */
+@FunctionalInterface
 public interface Builder<T> extends Serializable {
 
     T build(Object... options);

Mage/src/main/java/mage/filter/predicate/ObjectPlayerPredicate.java

@@ -32,5 +32,6 @@ package mage.filter.predicate;
  * @author North
  * @param <T>
  */
+@FunctionalInterface
 public interface ObjectPlayerPredicate<T extends ObjectPlayer> extends Predicate<T> {
 }

Mage/src/main/java/mage/filter/predicate/ObjectSourcePlayerPredicate.java

@@ -32,5 +32,6 @@ package mage.filter.predicate;
  * @author North
  * @param <T>
  */
+@FunctionalInterface
 public interface ObjectSourcePlayerPredicate<T extends ObjectSourcePlayer> extends ObjectPlayerPredicate<T> {
 }

Mage/src/main/java/mage/filter/predicate/Predicate.java

@@ -36,6 +36,7 @@ import mage.game.Game;
  * @author North
  * @param <T>
  */
+@FunctionalInterface
 public interface Predicate <T> extends Serializable {
     /**
      * Returns the result of applying this predicate to {@code input}. This method is <i>generally

Mage/src/main/java/mage/game/Table.java

@@ -64,6 +64,7 @@ public class Table implements Serializable {
     private Tournament tournament;
     private TableRecorder recorder;
 
+    @FunctionalInterface
     public interface TableRecorder {
         void record(Table table);
     }

Mage/src/main/java/mage/game/events/Listener.java

@@ -34,6 +34,7 @@ import java.io.Serializable;
  *
  * @author BetaSteward_at_googlemail.com
  */
+@FunctionalInterface
 public interface Listener<E extends ExternalEvent> extends Serializable {
     void event(E event);
 }

Mage/src/main/java/mage/util/CircularList.java

@@ -27,6 +27,8 @@
  */
 package mage.util;
 
+
+
 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Collection;

Mage/src/main/java/mage/util/Copyable.java

@@ -32,7 +32,7 @@ package mage.util;
  *
  * @author BetaSteward_at_googlemail.com
  */
+@FunctionalInterface
 public interface Copyable<T> {
-
     T copy();
 }

Mage/src/main/java/mage/util/functions/Function.java

@@ -30,6 +30,7 @@ package mage.util.functions;
 /**
  * @author nantuko
  */
+@FunctionalInterface
 public interface Function<X, Y> {
     X apply(Y in);
 }