Fix repositories listing by checking Gerrit repo with Optional

Gerrit v3.2 returns an empty Optional<ProjectState> instead of null.
Fix an issue where the GitHub projects listing was always returning
the empty list because the result of projects.get() was always not null.

Bug: Issue 12827
Change-Id: I41dba04e9bc3c2437ca72be135d4ec3612d8501a

github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/wizard/RepositoriesListController.java

diff --git a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/wizard/RepositoriesListController.java b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/wizard/RepositoriesListController.java
index bd069a8..2cf6170 100644
--- a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/wizard/RepositoriesListController.java
+++ b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/wizard/RepositoriesListController.java
@@ -67,7 +67,7 @@
       if (ghRepository.hasPushAccess() && ghRepository.hasPullAccess()) {
         JsonObject repository = new JsonObject();
         String projectName = organisation + "/" + ghRepository.getName();
-        if (projects.get(Project.NameKey.parse(projectName)) == null) {
+        if (!projects.get(Project.NameKey.parse(projectName)).isPresent()) {
           repository.add("name", new JsonPrimitive(ghRepository.getName()));
           repository.add("organisation", new JsonPrimitive(organisation));
           repository.add(