Provide a correct value for is_optional argument of ParamInfo constructor.

lib/html/scripts/systemhtml.py

 #!/usr/bin/python
 # 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.
 
 """This module provides shared functionality for the system to generate
 Dart:html APIs from the IDL database."""
 
 import emitter
 import os
@@ skipping 64 matching lines @@
     self.factory_provider_name = factory_provider_name
 
   def ConstructorInfo(self, interface_name):
     info = OperationInfo()
     info.overloads = None
     info.declared_name = interface_name
     info.name = interface_name
     info.constructor_name = self.name
     info.js_name = None
     info.type_name = interface_name
-    info.param_infos = map(lambda tXn: ParamInfo(tXn[1], None, tXn[0], 'null'),
+    info.param_infos = map(lambda tXn: ParamInfo(tXn[1], None, tXn[0], True),
                            self.opt_params)
     return info
 
 _html_element_constructors = {
   'AnchorElement' :
     ElementConstructorInfo(tag='a', opt_params=[('DOMString', 'href')]),
   'AreaElement': 'area',
   'ButtonElement': 'button',
   'BRElement': 'br',
   'BaseElement': 'base',
@@ skipping 1028 matching lines @@
 
     library_emitter = self._multiemitter.FileEmitter(library_file_path)
     library_file_dir = os.path.dirname(library_file_path)
     auxiliary_dir = os.path.relpath(auxiliary_dir, library_file_dir)
     imports_emitter = library_emitter.Emit(
         self._template, AUXILIARY_DIR=massage_path(auxiliary_dir))
     for path in sorted(self._path_to_emitter.keys()):
       relpath = os.path.relpath(path, library_file_dir)
       imports_emitter.Emit(
           "#source('$PATH');\n", PATH=massage_path(relpath))