Simplify RefByNameCacheWrapper

There is no need to excercise DynamicItem for content for each cache
operation as it cannot contain 'null' as its reference is set to
'NoOpRefByNameCache' when LibDbModule is loaded. All classes that refer
to 'RefByNameCacheWrapper' are loaded in this module too.
In case when 'LibSysModule' is not loaded (due to missing entry in
gerrit.config) then it doesn't matter as cache will not be created
anyway). In case when 'LibSysModule' is loaded then during the Gerrit
start DynamicItem value will be set to 'RefByNameGerritCache' instance
(which is a part of the same Module).
Note that RefByNameCacheWrapper is not a singleton therefore it will
evaluate DynamicItem once it gets crated together with
'CachedRefDatabase' instance each time when it is requested.

Change-Id: I80bc9ac417c8ac3ee6e5c6e1ae8637ed0e4023d3

src/main/java/com/googlesource/gerrit/plugins/gerritcachedrefdb/RefByNameCacheWrapper.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/gerritcachedrefdb/RefByNameCacheWrapper.java b/src/main/java/com/googlesource/gerrit/plugins/gerritcachedrefdb/RefByNameCacheWrapper.java
index c9744ad..9ce127a 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/gerritcachedrefdb/RefByNameCacheWrapper.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/gerritcachedrefdb/RefByNameCacheWrapper.java
@@ -24,22 +24,26 @@
 class RefByNameCacheWrapper implements RefByNameCache {
   private static final RefByNameCache NOOP_CACHE = new NoOpRefByNameCache();
 
-  @Inject(optional = true)
-  private DynamicItem<RefByNameCache> refByNameCache;
+  private final RefByNameCache cache;
+
+  @Inject
+  RefByNameCacheWrapper(DynamicItem<RefByNameCache> refByNameCache) {
+    this.cache = Optional.ofNullable(refByNameCache.get()).orElse(NOOP_CACHE);
+  }
 
   @Override
   public Ref computeIfAbsent(
       String identifier, String ref, Callable<? extends Optional<Ref>> loader) {
-    return cache().computeIfAbsent(identifier, ref, loader);
+    return cache.computeIfAbsent(identifier, ref, loader);
   }
 
   @Override
   public void evict(String identifier, String ref) {
-    cache().evict(identifier, ref);
+    cache.evict(identifier, ref);
   }
 
   @VisibleForTesting
   RefByNameCache cache() {
-    return Optional.ofNullable(refByNameCache).map(DynamicItem::get).orElse(NOOP_CACHE);
+    return cache;
   }
 }