A method or accessor with empty body is implicitly abstract.

dart/lib/compiler/implementation/ssa/builder.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.
 
 part of ssa;
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
@@ skipping 952 matching lines @@
    * creates a new constructor body, if none can be found.
    *
    * Returns [:null:] if the constructor does not have a body.
    */
   ConstructorBodyElement getConstructorBody(FunctionElement constructor) {
     assert(constructor.isGenerativeConstructor());
     assert(invariant(constructor, constructor.isImplementation));
     if (constructor is SynthesizedConstructorElement) return null;
     FunctionExpression node = constructor.parseNode(compiler);
     // If we know the body doesn't have any code, we don't generate it.
-    if (node.body.asBlock() != null) {
-      NodeList statements = node.body.asBlock().statements;
-      if (statements.isEmpty) return null;
-    }
+    if (!node.hasBody()) return null;
+    if (node.hasEmptyBody()) return null;
     ClassElement classElement = constructor.getEnclosingClass();
     ConstructorBodyElement bodyElement;
     for (Link<Element> backendMembers = classElement.backendMembers;
          !backendMembers.isEmpty;
          backendMembers = backendMembers.tail) {
       Element backendMember = backendMembers.head;
       if (backendMember.isGenerativeConstructorBody()) {
         ConstructorBodyElement body = backendMember;
         if (body.constructor == constructor) {
           bodyElement = backendMember;
@@ skipping 3599 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }