cache

diff --git a/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java b/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java
index ef65574..89869c6 100644
--- a/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java
+++ b/src/main/java/br/ufrgs/inf/prosoft/cache/Caffeine.java
@@ -5,19 +5,22 @@
  */
 package br.ufrgs.inf.prosoft.cache;
 
-import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
 
 /**
  *
  * @author root
+ * @param <K>
+ * @param <V>
  */
 public class Caffeine<K, V> implements Cache<K, V> {
 
     private static final boolean CACHE_EVALUATE_PERFORMANCE = System.getenv("CACHE_EVENTS") == null || !System.getenv("CACHE_EVENTS").equals("false");
     private static final boolean CACHE_REGISTER_SIZE = System.getenv("CACHE_REGISTER_SIZE") != null && System.getenv("CACHE_REGISTER_SIZE").equals("true");
-    private final com.github.benmanes.caffeine.cache.Cache<K, V> cache;
+    private final com.github.benmanes.caffeine.cache.Cache<Optional<K>, Optional<V>> cache;
     private final CachePerformance cachePerformance;
 
     public Caffeine() {
@@ -80,24 +83,24 @@ public class Caffeine<K, V> implements Cache<K, V> {
 
     @Override
     public void put(K key, V value) {
-        this.cache.put(key, value);
+        this.cache.put(Optional.ofNullable(key), Optional.ofNullable(value));
         registerEvent(EventType.ADDITION, value);
     }
 
     @Override
     public V get(K key) throws KeyNotFoundException {
-        V get = this.cache.getIfPresent(key);
+        Optional<V> get = this.cache.getIfPresent(Optional.ofNullable(key));
         if (get == null) {
             registerEvent(EventType.MISS, key);
             throw new KeyNotFoundException();
         }
         registerEvent(EventType.HIT, get);
-        return get;
+        return get.orElse(null);
     }
 
     @Override
     public void invalidate(K key) {
-        this.cache.invalidate(key);
+        this.cache.invalidate(Optional.ofNullable(key));
         registerEvent(EventType.INVALIDATION, null);
     }
 
@@ -121,6 +124,8 @@ public class Caffeine<K, V> implements Cache<K, V> {
     }
 
     public List<V> values() {
-        return new ArrayList<>(this.cache.asMap().values());
+        return this.cache.asMap().values().stream()
+                .map(value -> value.orElse(null))
+                .collect(Collectors.toList());
     }
 }

diff --git a/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java b/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java
index 5d3f2c4..e036f6c 100644
--- a/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java
+++ b/src/main/java/br/ufrgs/inf/prosoft/cache/CaffeineGetterCache.java
@@ -12,7 +12,7 @@ import java.util.function.Supplier;
  * @author root
  * @param <V>
  */
-public class CaffeineGetterCache<V> extends CaffeineSingleCache<String, V> {
+public class CaffeineGetterCache<V> extends CaffeineSingleCache<Void, V> {
 
     public CaffeineGetterCache(String name) {
         super(name);
@@ -31,27 +31,27 @@ public class CaffeineGetterCache<V> extends CaffeineSingleCache<String, V> {
     }
 
     public void put(V value, long timeToLive) {
-        super.put("", value, timeToLive);
+        super.put(null, value, timeToLive);
     }
 
     public void put(V value) {
-        super.put("", value);
+        super.put(null, value);
     }
 
     public V get() throws KeyNotFoundException {
-        return super.get("");
+        return super.get(null);
     }
 
     public void invalidate() {
-        super.invalidate("");
+        super.invalidate(null);
     }
 
     public V computeIfAbsent(Supplier<V> supplier, long timeToLive) {
-        return super.computeIfAbsent("", supplier, timeToLive);
+        return super.computeIfAbsent(null, supplier, timeToLive);
     }
 
     public V computeIfAbsent(Supplier<V> supplier) {
-        return super.computeIfAbsent("", supplier);
+        return super.computeIfAbsent(null, supplier);
     }
 
 }