Avoid NoSuchElementException "No value present"

When parsing the response from Cache#getIfPresent we end up in states
where EiffelEventIdCache#getEventIdIfPresent throws
NoSuchElementException.
Rewrite the conversion from @Nullable Optional<UUID> to Optional<UUID>
to be more clear to avoid this or at least get a clear indication of
exactly what happens.

Solves: Jira GER-1612
Change-Id: I3668c29aa284674a0cf8e36be80162f4d1bf71eb

src/main/java/com/googlesource/gerrit/plugins/eventseiffel/cache/EiffelEventIdCacheImpl.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/eventseiffel/cache/EiffelEventIdCacheImpl.java b/src/main/java/com/googlesource/gerrit/plugins/eventseiffel/cache/EiffelEventIdCacheImpl.java
index 3bc237d..5377521 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/eventseiffel/cache/EiffelEventIdCacheImpl.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/eventseiffel/cache/EiffelEventIdCacheImpl.java
@@ -94,7 +94,11 @@
   }
 
   private Optional<UUID> getEventIdIfPresent(EventKey key) {
-    return Optional.ofNullable(eventIds.getIfPresent(key)).map(Optional::get);
+    Optional<UUID> fromCache = eventIds.getIfPresent(key);
+    if (fromCache == null) {
+      return Optional.empty();
+    }
+    return fromCache;
   }
 
   @Override