Adapt to ProjectCache#get interface change

Change-Id: I73717b09c4f482bf6d84a11be3450d16b5bee0b1

src/main/java/com/googlesource/gerrit/plugins/webhooks/rest/ProjectsCollection.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/webhooks/rest/ProjectsCollection.java b/src/main/java/com/googlesource/gerrit/plugins/webhooks/rest/ProjectsCollection.java
index a31f99c..5e1d54d 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/webhooks/rest/ProjectsCollection.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/webhooks/rest/ProjectsCollection.java
@@ -53,7 +53,7 @@
 
   private ProjectWebhooksResource parse(String id) throws ResourceNotFoundException {
     Project.NameKey n = Project.nameKey(id);
-    if (projectCache.get(n) != null) {
+    if (projectCache.get(n).isPresent()) {
       return new ProjectWebhooksResource(Project.nameKey(id));
     }
     throw new ResourceNotFoundException(String.format("Project %s does not exist", id));