Make isEmpty a getter.

samples/markdown/html_renderer.dart

 // Copyright (c) 2011, 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.
 
 String renderToHtml(List<Node> nodes) => new HtmlRenderer().render(nodes);
 
 /// Translates a parsed AST to HTML.
 class HtmlRenderer implements NodeVisitor {
   static const _BLOCK_TAGS = const RegExp(
       'blockquote|h1|h2|h3|h4|h5|h6|hr|p|pre');
 
   StringBuffer buffer;
 
   HtmlRenderer();
 
   String render(List<Node> nodes) {
     buffer = new StringBuffer();
 
     for (final node in nodes) node.accept(this);
 
     return buffer.toString();
   }
 
   void visitText(Text text) {
     buffer.add(text.text);
   }
 
   bool visitElementBefore(Element element) {
     // Hackish. Separate block-level elements with newlines.
-    if (!buffer.isEmpty() &&
+    if (!buffer.isEmpty &&
         _BLOCK_TAGS.firstMatch(element.tag) != null) {
       buffer.add('\n');
     }
 
     buffer.add('<${element.tag}');
 
     for (final name in element.attributes.getKeys()) {
       buffer.add(' $name="${element.attributes[name]}"');
     }
 
     if (element.isEmpty) {
       // Empty element like <hr/>.
       buffer.add(' />');
       return false;
     } else {
       buffer.add('>');
       return true;
     }
   }
 
   void visitElementAfter(Element element) {
     buffer.add('</${element.tag}>');
   }
 }