Add missing format specifier to String.format

Change-Id: I32eaf2832c73003d3285643543376b44f1b9b4eb
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/plugins/PluginLoader.java b/gerrit-server/src/main/java/com/google/gerrit/server/plugins/PluginLoader.java
index 08dba3a..ee27de3 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/plugins/PluginLoader.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/plugins/PluginLoader.java
@@ -508,7 +508,7 @@
       return loadJsPlugin(name, srcPlugin, snapshot);
     } else {
       throw new InvalidPluginException(String.format(
-          "Unsupported plugin type: ", srcPlugin.getName()));
+          "Unsupported plugin type: %s", srcPlugin.getName()));
     }
   }