Fix issue with new project indexing

Project cache implementation returns Optional, to check if project is up
to date we have to check if Optional is present instead of null.

Bug: Issue 12794
Change-Id: Ib311716ad0ff62ed585ae59cc062b750eba06dac
diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/index/ProjectCheckerImpl.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/index/ProjectCheckerImpl.java
index 548ccc0..d9851f3 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/index/ProjectCheckerImpl.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/index/ProjectCheckerImpl.java
@@ -28,6 +28,6 @@
 
   @Override
   public boolean isProjectUpToDate(Project.NameKey projectName) {
-    return projectCache.get(projectName) != null;
+    return projectCache.get(projectName).isPresent();
   }
 }