Getters should not have parameters.

pkg/analysis_server/lib/src/computer/computer_outline.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 computer.outline;
 
 import 'package:analysis_server/src/collections.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
@@ skipping 280 matching lines @@
     FormalParameterList parameters = method.parameters;
     ElementKind kind;
     if (method.isGetter) {
       kind = ElementKind.GETTER;
     } else if (method.isSetter) {
       kind = ElementKind.SETTER;
     } else {
       kind = ElementKind.METHOD;
     }
     _SourceRegion sourceRegion = _getSourceRegion(method);
-    String parametersStr = parameters != null ? parameters.toSource() : '';
+    String parametersStr = parameters != null ? parameters.toSource() : null;
     String returnTypeStr = returnType != null ? returnType.toSource() : '';
     Element element = new Element(
         kind,
         name,
         Element.makeFlags(
             isPrivate: Identifier.isPrivateName(name),
             isDeprecated: _isDeprecated(method),
             isAbstract: method.isAbstract,
             isStatic: method.isStatic),
         location: _getLocationNode(nameNode),
@@ skipping 69 matching lines @@
 
 
 /**
  * A range of characters.
  */
 class _SourceRegion {
   final int length;
   final int offset;
   _SourceRegion(this.offset, this.length);
 }