Use static final empty Modifier instead of null.

lib/compiler/implementation/js_backend/emitter.dart

 // 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.
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
 class ClosureInvocationElement extends FunctionElement {
   ClosureInvocationElement(SourceString name,
@@ skipping 479 matching lines @@
     }
   }
 
   bool instanceFieldNeedsGetter(Element member) {
     assert(member.isField());
     return compiler.codegenWorld.hasInvokedGetter(member, compiler);
   }
 
   bool instanceFieldNeedsSetter(Element member) {
     assert(member.isField());
-    return (member.modifiers === null || !member.modifiers.isFinalOrConst())
+    return (!member.modifiers.isFinalOrConst())
         && compiler.codegenWorld.hasInvokedSetter(member, compiler);
   }
 
   String compiledFieldName(Element member) {
     assert(member.isField());
     return member.isNative()
         ? member.name.slowToString()
         : namer.getName(member);
   }
 
   /**
    * Documentation wanted -- johnniwinther
    *
    * Invariant: [member] must be a declaration element.
    */
   void addInstanceMember(Element member,
                          DefineMemberFunction defineInstanceMember) {
     assert(invariant(member, member.isDeclaration));
     // TODO(floitsch): we don't need to deal with members of
     // uninstantiated classes, that have been overwritten by subclasses.
 
     if (member.isFunction()
         || member.isGenerativeConstructorBody()
         || member.isGetter()
         || member.isSetter()) {
-      if (member.modifiers !== null && member.modifiers.isAbstract()) return;
+      if (member.modifiers.isAbstract()) return;
       CodeBuffer codeBuffer = compiler.codegenWorld.generatedCode[member];
       if (codeBuffer == null) return;
       defineInstanceMember(namer.getName(member), codeBuffer);
       codeBuffer = compiler.codegenWorld.generatedBailoutCode[member];
       if (codeBuffer !== null) {
         defineInstanceMember(namer.getBailoutName(member), codeBuffer);
       }
       FunctionElement function = member;
       FunctionSignature parameters = function.computeSignature(compiler);
       if (!parameters.optionalParameters.isEmpty()) {
@@ skipping 898 matching lines @@
 const String HOOKS_API_USAGE = """
 // Generated by dart2js, the Dart to JavaScript compiler.
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;