Fix bad assert in constant evaluation.

runtime/vm/parser.cc

 // Copyright (c) 2012, 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/parser.h"
 
 #include "lib/invocation_mirror.h"
 #include "platform/utils.h"
 #include "vm/ast_transformer.h"
 #include "vm/bootstrap.h"
@@ skipping 13437 matching lines @@
     LocalScope* empty_scope = new(Z) LocalScope(NULL, 0, 0);
     SequenceNode* seq = new(Z) SequenceNode(expr->token_pos(), empty_scope);
     seq->Add(ret);
 
     Object& result = Object::Handle(Z, Compiler::ExecuteOnce(seq));
     if (result.IsError()) {
       ReportErrors(Error::Cast(result),
                    script_, expr_pos,
                    "error evaluating constant expression");
     }
-    ASSERT(result.IsInstance());
+    ASSERT(result.IsInstance() || result.IsNull());
     Instance& value = Instance::ZoneHandle(Z);
     value ^= result.raw();
     value = TryCanonicalize(value, TokenPos());
     return value;
   }
 }
 
 
 void Parser::SkipFunctionLiteral() {
   if (IsIdentifier()) {
@@ skipping 342 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart