Add null check.

lib/compiler/implementation/tree/unparser.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.
 
 class Unparser implements Visitor {
   StringBuffer sb;
 
   Unparser();
 
   String unparse(Node node) {
@@ skipping 72 matching lines @@
 
   visitFunctionExpression(FunctionExpression node) {
     if (node.returnType !== null) {
       visit(node.returnType);
       sb.add(' ');
     }
     // TODO(antonm): that's a workaround as currently FunctionExpression
     // names are modelled with Send and it emits operator[] as only
     // operator, without [] which are expected to be emitted with
     // arguments.
-    Send send = node.name.asSend();
-    if (send !== null) {
+    if (node.name is Send) {
+      Send send = node.name;
       assert(send is !SendSet);
       visit(send.receiver);
       visit(send.selector);
     } else {
       visit(node.name);
     }
     visit(node.parameters);
     visit(node.body);
   }
 
@@ skipping 338 matching lines @@
       sb.add(' ');
     }
     visit(node.name);
     if (node.typeParameters !== null) {
       visit(node.typeParameters);
     }
     visit(node.formals);
     add(node.endToken.value);
   }
 }