Shorter encoding for zero optional arguments.

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
index 846ce8bd2593455d3a28ca66acc18e67cd011c5e..1b7beca01128d80d4827b02b3bfdcfc47b111e52 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
@@ -833,6 +833,9 @@ class FragmentEmitter {
     // TODO(herhut): Replace [js.LiteralNull] with [js.ArrayHole].
     if (method.optionalParameterDefaultValues is List) {
       List<ConstantValue> defaultValues = method.optionalParameterDefaultValues;
+      if (defaultValues.isEmpty) {
+        return new js.LiteralNull();
+      }
       Iterable<js.Expression> elements =
           defaultValues.map(generateConstantReference);
       return js.js('function() { return #; }',