Fix breakage in printing.

runtime/vm/object.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "vm/assembler.h"
 #include "vm/assert.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
@@ skipping 2445 matching lines @@
 
 RawTypeArguments* TypeArguments::NewInstantiatedTypeArguments(
     const TypeArguments& uninstantiated_type_arguments,
     const TypeArguments& instantiator_type_arguments) {
   return InstantiatedTypeArguments::New(uninstantiated_type_arguments,
                                         instantiator_type_arguments);
 }
 
 
 const char* TypeArguments::ToCString() const {
-  // TypeArguments is an abstract class.
+  // TypeArguments is an abstract class, however it may wrap a null.
+  if (IsNull()) {
+    return "NULL TypeArguments";
+  }
   UNREACHABLE();
   return "TypeArguments";
 }
 
 
 intptr_t TypeArray::Length() const {
   ASSERT(!IsNull());
   return Smi::Value(raw_ptr()->length_);
 }
 
@@ skipping 4780 matching lines @@
   const String& str = String::Handle(pattern());
   const char* format = "JSRegExp: pattern=%s flags=%s";
   intptr_t len = OS::SNPrint(NULL, 0, format, str.ToCString(), Flags());
   char* chars = reinterpret_cast<char*>(
       Isolate::Current()->current_zone()->Allocate(len + 1));
   OS::SNPrint(chars, (len + 1), format, str.ToCString(), Flags());
   return chars;
 }
 
 }  // namespace dart