anchor.diff:        addCompileTimeError(
             token.charOffset, "const field must have initializer.");
         // Creating a null value to prevent the Dart VM from crashing.
  -      push(new NullLiteral()..fileOffset = token.charOffset);
  +      push(astFactory.nullLiteral(token));
       } else {
         push(NullValue.FieldInitializer);
       }
  
positive.code:           library.uri.path == "_builtin" &&
            member?.name == "_getMainClosure") {
          // TODO(ahe): https://github.com/dart-lang/sdk/issues/28989
          return new NullLiteral()..fileOffset = offsetForToken(token);
        } else {
          return new UnresolvedAccessor(this, n, token);
        }
  
negative.code:   @override
    void handleLiteralNull(Token token) {
      debugEvent("LiteralNull");
      push(astFactory.nullLiteral(token));
    }
  
    @override
  