Scripts shouldn't add a non-null check in dart2js for a nullable parameter (seeWebGl.texImage2D)

tools/dom/scripts/htmldartgenerator.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
 from generator import AnalyzeOperation, ConstantOutputOrder, \
@@ skipping 402 matching lines @@
           converts_null = \
               ('TreatNullAs' in argument.ext_attrs) or \
               (argument.default_value is not None) or \
               (argument.default_value_is_null)
           if argument.type.nullable or converts_null or not typechecked:
             checks.append('(%s is %s || %s == null)' % (
                 parameter_name, test_type, parameter_name))
           else:
             checks.append('(%s is %s)' % (
                 parameter_name, test_type))
-        elif i >= number_of_required_in_dart:
+        elif i >= number_of_required_in_dart and not argument.type.nullable:
           checks.append('%s != null' % parameter_name)
 
       # There can be multiple presence checks.  We need them all since a later
       # optional argument could have been passed by name, leaving 'holes'.
       checks.extend(['%s == null' % name for name in parameter_names[argument_count:]])
 
       GenerateCall(signature_index, argument_count, checks)
 
     # TODO: Optimize the dispatch to avoid repeated checks.
     if len(signatures) > 1:
@@ skipping 454 matching lines @@
   def _InputType(self, type_name, info):
     conversion = self._InputConversion(type_name, info.declared_name)
     if conversion:
       return conversion.input_type
     else:
       # If typedef it's a union return dynamic.
       if self._database.HasTypeDef(type_name):
         return 'dynamic'
       else:
         return self._NarrowInputType(type_name) if type_name else 'dynamic'