Change analysis server protocol to omit empty lists when optional.

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/protocol2.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 146 matching lines @@
       List<Outline> classContents) {
     SimpleIdentifier nameNode = classDeclaration.name;
     String name = nameNode.name;
     _SourceRegion sourceRegion = _getSourceRegion(classDeclaration);
     Element element = new Element(ElementKind.CLASS, name,
         Element.makeFlags(isPrivate: Identifier.isPrivateName(name),
             isDeprecated: _isDeprecated(classDeclaration),
             isAbstract: classDeclaration.isAbstract),
         location: _getLocationNode(nameNode));
     return new Outline(element, sourceRegion.offset,
-        sourceRegion.length,
-        children: classContents.isNotEmpty ? classContents : null);
+        sourceRegion.length, children: classContents);
   }
 
   Outline _newClassTypeAlias(ClassTypeAlias alias) {
     SimpleIdentifier nameNode = alias.name;
     String name = nameNode.name;
     _SourceRegion sourceRegion = _getSourceRegion(alias);
     Element element = new Element(ElementKind.CLASS_TYPE_ALIAS, name,
         Element.makeFlags(isPrivate: Identifier.isPrivateName(name),
             isDeprecated: _isDeprecated(alias), isAbstract: alias.isAbstract),
         location: _getLocationNode(nameNode));
@@ skipping 18 matching lines @@
     _SourceRegion sourceRegion = _getSourceRegion(constructor);
     FormalParameterList parameters = constructor.parameters;
     String parametersStr = parameters != null ? parameters.toSource() : '';
     Element element = new Element(ElementKind.CONSTRUCTOR, name,
         Element.makeFlags(isPrivate: isPrivate,
             isDeprecated: _isDeprecated(constructor)),
         location: _getLocationOffsetLength(offset, length),
         parameters: parametersStr);
     List<Outline> contents = _addLocalFunctionOutlines(constructor.body);
     Outline outline = new Outline(element, sourceRegion.offset,
-        sourceRegion.length, children: contents.isNotEmpty ? contents : null);
+        sourceRegion.length, children: contents);
     return outline;
   }
 
   Outline _newFunctionOutline(FunctionDeclaration function, bool isStatic) {
     TypeName returnType = function.returnType;
     SimpleIdentifier nameNode = function.name;
     String name = nameNode.name;
     FunctionExpression functionExpression = function.functionExpression;
     FormalParameterList parameters = functionExpression.parameters;
     ElementKind kind;
     if (function.isGetter) {
       kind = ElementKind.GETTER;
     } else if (function.isSetter) {
       kind = ElementKind.SETTER;
     } else {
       kind = ElementKind.FUNCTION;
     }
     _SourceRegion sourceRegion = _getSourceRegion(function);
     String parametersStr = parameters != null ? parameters.toSource() : '';
     String returnTypeStr = returnType != null ? returnType.toSource() : '';
     Element element = new Element(kind, name,
         Element.makeFlags(isPrivate: Identifier.isPrivateName(name),
             isDeprecated: _isDeprecated(function), isStatic: isStatic),
         location: _getLocationNode(nameNode), parameters: parametersStr,
         returnType: returnTypeStr);
     List<Outline> contents = _addLocalFunctionOutlines(functionExpression.body);
     Outline outline = new Outline(element, sourceRegion.offset,
-        sourceRegion.length, children: contents.isNotEmpty ? contents : null);
+        sourceRegion.length, children: contents);
     return outline;
   }
 
   Outline _newFunctionTypeAliasOutline(FunctionTypeAlias alias) {
     TypeName returnType = alias.returnType;
     SimpleIdentifier nameNode = alias.name;
     String name = nameNode.name;
     _SourceRegion sourceRegion = _getSourceRegion(alias);
     FormalParameterList parameters = alias.parameters;
     String parametersStr = parameters != null ? parameters.toSource() : '';
@@ skipping 23 matching lines @@
     _SourceRegion sourceRegion = _getSourceRegion(method);
     String parametersStr = parameters != null ? parameters.toSource() : '';
     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),
         parameters: parametersStr, returnType: returnTypeStr);
     List<Outline> contents = _addLocalFunctionOutlines(method.body);
     Outline outline = new Outline(element, sourceRegion.offset,
-        sourceRegion.length, children: contents.isNotEmpty ? contents : null);
+        sourceRegion.length, children: contents);
     return outline;
   }
 
   Outline _newUnitOutline(List<Outline> unitContents) {
     Element element = new Element(ElementKind.COMPILATION_UNIT, '<unit>',
         Element.makeFlags(), location: _getLocationNode(_unit));
     return new Outline(element, _unit.offset, _unit.length,
-        children: unitContents.isNotEmpty ? unitContents : null);
+        children: unitContents);
   }
 
   Outline _newVariableOutline(String typeName, ElementKind kind,
       VariableDeclaration variable, bool isStatic) {
     SimpleIdentifier nameNode = variable.name;
     String name = nameNode.name;
     _SourceRegion sourceRegion = _getSourceRegion(variable);
     Element element = new Element(kind, name,
         Element.makeFlags(isPrivate: Identifier.isPrivateName(name),
             isDeprecated: _isDeprecated(variable),
@@ skipping 32 matching lines @@
 
 
 /**
  * A range of characters.
  */
 class _SourceRegion {
   final int length;
   final int offset;
   _SourceRegion(this.offset, this.length);
 }