Workaround for ConstantVisitor dependency issues.

pkg/docgen/lib/src/models/annotation.dart

 // Copyright (c) 2014, 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.
 
 library docgen.models.annotation;
 
 import '../exports/source_mirrors.dart';
 
 import '../exports/dart2js_mirrors.dart' show ResolvedNode;
 
@@ skipping 65 matching lines @@
                 identical(beginToken.stringValue, opString)) {
               sb.write(' ');
             }
           }
     }
     recursionLevel++;
     visit(node.argumentsNode);
     recursionLevel--;
   }
 
-  unparseNodeListFrom(NodeList node, var from, {spaces}) {
+  unparseNodeListFrom(NodeList node, var from, {bool spaces: true}) {
     if (from.isEmpty) return;
 
     visit(from.head);
 
     for (var link = from.tail; !link.isEmpty; link = link.tail) {
       if (recursionLevel >= 2) {
         parameterValueCallback(sb.toString());
         sb.clear();
       }
       visit(link.head);
     }
     if (recursionLevel >= 2) {
       parameterValueCallback(sb.toString());
       sb.clear();
     }
   }
 
   visitNodeList(NodeList node) {
     addToken(node.beginToken);
     if (recursionLevel == 1) sb.clear();
     if (node.nodes != null) {
       recursionLevel++;
       unparseNodeListFrom(node, node.nodes);
       recursionLevel--;
     }
     if (node.endToken != null) write(node.endToken.value);
   }
 }