StreamEventsApiListener: Prevent NPE when account is null

This happens when account is null and some plugin wants to convert the
account data to an account attribute from the event. This account is
null, for example, if the change-abandoned event is generated on the
auto cleanup inside Gerrit Core.

Change-Id: Id4595208d3745988ec6c6008ea4506fd4e9ff7eb
Signed-off-by: Remy Bohmer <linux@bohmer.net>
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/events/StreamEventsApiListener.java b/gerrit-server/src/main/java/com/google/gerrit/server/events/StreamEventsApiListener.java
index 5294391..a5fe0a6 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/events/StreamEventsApiListener.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/events/StreamEventsApiListener.java
@@ -177,8 +177,8 @@
         new Supplier<AccountAttribute>() {
           @Override
           public AccountAttribute get() {
-            return eventFactory.asAccountAttribute(
-                new Account.Id(account._accountId));
+            return account != null ? eventFactory.asAccountAttribute(
+                new Account.Id(account._accountId)) : null;
           }
         });
   }