src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/OptimizationPlugin.java

@@ -271,11 +271,11 @@
                 optimizers.add(new ForNameFolding());
                 break;
             } else if (s.equals(FORNAME_REMOVAL)) {
                 optimizers.add(new ForNameFolding());
             } else {
-                throw new PluginException("Unknown optimization");
+                throw new IllegalArgumentException("Unknown optimization: " + s);
             }
         }
         String f = config.get(LOG);
         if (f != null) {
             try {