Remove usage of java.util.Optional

Gerrit 2.13 uses java 7 so replace java optional by guava one. This
commit needs to be reverted when merging up to 2.14.

Change-Id: Iafed1431ea9aaa85d0441473d03d0ab0dc0cefd0
diff --git a/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsConfig.java b/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsConfig.java
index 7567855..c29ae7f 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsConfig.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsConfig.java
@@ -14,13 +14,13 @@
 
 package com.googlesource.gerrit.plugins.quota;
 
+import com.google.common.base.Optional;
 import com.google.common.collect.ArrayTable;
 import com.google.common.collect.Table;
 import java.text.MessageFormat;
 import java.util.Arrays;
 import java.util.Locale;
 import java.util.Map;
-import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.regex.Matcher;
@@ -183,8 +183,8 @@
    */
   Optional<Map<String, RateLimit>> getRatelimits(Type type) {
     if (rateLimits != null) {
-      return Optional.ofNullable(rateLimits.row(type));
+      return Optional.fromNullable(rateLimits.row(type));
     }
-    return Optional.empty();
+    return Optional.absent();
   }
 }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsFinder.java b/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsFinder.java
index 751735c..2cf7d6f 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsFinder.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/quota/AccountLimitsFinder.java
@@ -15,6 +15,7 @@
 
 import static com.googlesource.gerrit.plugins.quota.AccountLimitsConfig.KEY;
 
+import com.google.common.base.Optional;
 import com.google.gerrit.common.data.GroupDescription;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.account.GroupMembership;
@@ -30,7 +31,6 @@
 import org.slf4j.LoggerFactory;
 
 import java.util.Map;
-import java.util.Optional;
 
 public class AccountLimitsFinder {
   private static final Logger log =
@@ -64,11 +64,11 @@
           log.error("Ignoring limits for unknown group ''{}'' in quota.config",
               groupName);
         } else if (memberShip.contains(d.getGroupUUID())) {
-          return Optional.ofNullable(limits.get().get(groupName));
+          return Optional.fromNullable(limits.get().get(groupName));
         }
       }
     }
-    return Optional.empty();
+    return Optional.absent();
   }
 
   /**
@@ -78,9 +78,9 @@
    */
   public Optional<RateLimit> getRateLimit(Type type, String groupName) {
     if (getRatelimits(type).isPresent()) {
-      return Optional.ofNullable(getRatelimits(type).get().get(groupName));
+      return Optional.fromNullable(getRatelimits(type).get().get(groupName));
     }
-    return Optional.empty();
+    return Optional.absent();
   }
 
   /**
diff --git a/src/main/java/com/googlesource/gerrit/plugins/quota/Module.java b/src/main/java/com/googlesource/gerrit/plugins/quota/Module.java
index 935498a..240f42e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/quota/Module.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/quota/Module.java
@@ -19,6 +19,7 @@
 import static com.google.gerrit.server.project.ProjectResource.PROJECT_KIND;
 import static com.googlesource.gerrit.plugins.quota.QuotaResource.QUOTA_KIND;
 
+import com.google.common.base.Optional;
 import com.google.common.cache.CacheLoader;
 import com.google.common.util.concurrent.RateLimiter;
 import com.google.gerrit.extensions.events.GarbageCollectorListener;
@@ -39,7 +40,6 @@
 import com.google.inject.Scopes;
 import com.google.inject.internal.UniqueAnnotations;
 import com.googlesource.gerrit.plugins.quota.AccountLimitsConfig.RateLimit;
-import java.util.Optional;
 import org.eclipse.jgit.transport.PostReceiveHook;
 
 class Module extends CacheModule {