Compare to `None` using identity `is` operator

This is a trivial change that replaces `==` operator with `is` operator, following PEP 8 guideline:

> Comparisons to singletons like None should always be done with is or is not, never the equality operators.

https://legacy.python.org/dev/peps/pep-0008/#programming-recommendations
diff --git a/scripts/helper_file_generator.py b/scripts/helper_file_generator.py
index 9e095fb..4f1bd37 100644
--- a/scripts/helper_file_generator.py
+++ b/scripts/helper_file_generator.py
@@ -192,7 +192,7 @@
         if self.helper_file_type == 'enum_string_header':
             value_set = set()
             for elem in groupElem.findall('enum'):
-                if elem.get('supported') != 'disabled' and elem.get('alias') == None:
+                if elem.get('supported') != 'disabled' and elem.get('alias') is None:
                     value_set.add(elem.get('name'))
             self.enum_output += self.GenerateEnumStringConversion(groupName, value_set)
         elif self.helper_file_type == 'object_types_header':
@@ -428,7 +428,7 @@
         for item in self.structMembers:
             if self.NeedSafeStruct(item) == True:
                 safe_struct_header += '\n'
-                if item.ifdef_protect != None:
+                if item.ifdef_protect is not None:
                     safe_struct_header += '#ifdef %s\n' % item.ifdef_protect
                 safe_struct_header += 'struct safe_%s {\n' % (item.name)
                 for member in item.members:
@@ -454,7 +454,7 @@
                 safe_struct_header += '    %s *ptr() { return reinterpret_cast<%s *>(this); }\n' % (item.name, item.name)
                 safe_struct_header += '    %s const *ptr() const { return reinterpret_cast<%s const *>(this); }\n' % (item.name, item.name)
                 safe_struct_header += '};\n'
-                if item.ifdef_protect != None:
+                if item.ifdef_protect is not None:
                     safe_struct_header += '#endif // %s\n' % item.ifdef_protect
         return safe_struct_header
     #
@@ -805,7 +805,7 @@
                 continue
             if item.name in wsi_structs:
                 continue
-            if item.ifdef_protect != None:
+            if item.ifdef_protect is not None:
                 safe_struct_body.append("#ifdef %s\n" % item.ifdef_protect)
             ss_name = "safe_%s" % item.name
             init_list = ''          # list of members in struct constructor initializer
@@ -1116,7 +1116,7 @@
             init_copy = copy_construct_init.replace('src.', 'src->')
             init_construct = copy_construct_txt.replace('src.', 'src->')
             safe_struct_body.append("\nvoid %s::initialize(const %s* src)\n{\n%s%s}" % (ss_name, ss_name, init_copy, init_construct))
-            if item.ifdef_protect != None:
+            if item.ifdef_protect is not None:
                 safe_struct_body.append("#endif // %s\n" % item.ifdef_protect)
         return "\n".join(safe_struct_body)
     #
@@ -1208,7 +1208,7 @@
             if not info:
                 continue
 
-            if item.ifdef_protect != None:
+            if item.ifdef_protect is not None:
                 code.append('#ifdef %s' % item.ifdef_protect)
 
             code.append('// Map type {} to id {}'.format(typename, info.value))
@@ -1216,7 +1216,7 @@
                 id_decl=id_decl, id_member=id_member))
             code.append(idmap_format.format(template=idmap, typename=typename, id_value=info.value, typedef=type_member))
 
-            if item.ifdef_protect != None:
+            if item.ifdef_protect is not None:
                 code.append('#endif // %s' % item.ifdef_protect)
 
         # Generate utilities for all types