Address review comments in commited cl (issue 10460002).

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
===================================================================
--- runtime/vm/flow_graph_builder.cc	(revision 8115)
+++ runtime/vm/flow_graph_builder.cc	(working copy)
@@ -1326,7 +1326,7 @@
   ASSERT(function.context_scope() != ContextScope::null());
 
   // The function type of a closure may have type arguments. In that case, pass
-  // the type arguments of the instantiator.
+  // the type arguments of the instantiator. Otherwise, pass null object.
   const Class& cls = Class::Handle(function.signature_class());
   ASSERT(!cls.IsNull());
   const bool requires_type_arguments = cls.HasTypeArguments();
@@ -1334,6 +1334,8 @@
   if (requires_type_arguments) {
     ASSERT(!function.IsImplicitStaticClosureFunction());
     type_arguments = BuildInstantiatorTypeArguments(node->token_index(), NULL);
+  } else {
+    type_arguments = BuildNullValue();
   }
 
   CreateClosureComp* create =