Log a warning when url is not defined in a remote section

Change-Id: I484cf20d73416be40dc4aa900b11b001e9b432af
diff --git a/src/main/java/com/googlesource/gerrit/plugins/webhooks/EventHandler.java b/src/main/java/com/googlesource/gerrit/plugins/webhooks/EventHandler.java
index b0a39e5..d501cf4 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/webhooks/EventHandler.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/webhooks/EventHandler.java
@@ -64,6 +64,7 @@
     for (String name : cfg.getSubsections("remote")) {
       String url = cfg.getString("remote", name, "url");
       if (Strings.isNullOrEmpty(url)) {
+        log.warn("remote.{}.url not defined, skipping this remote", name);
         continue;
       }