Bad syntax of expression in ng-class?

Question

I am learning Angular.js and I have this piece of code:

<button ng-class="{'btn pull-left', 
duplicatesInList === true ? 'btn-warning': 'btn-success'}" 
id="saveScoreButton" type="button" ng-click="add()"><button>

And something is wrong with syntax but I have no idea what... What I want to do is find duplicates in list, and when there is a duplicate I want to warn user by change save button style (class btn-warning). I will be very happy in anybody decides to help me, thank you in advance. Update: Console log:

Error: [$parse:syntax] http://errors.angularjs.org/1.2.16/$parse/syntax?p0=%2C&p1=is%20unexpected%2C%20expecting%20%5B%3A%5D&p2=17&p3=%7B'btn%20pull-left'%2CNaNuplicatesInList%20%3D%3D%3D%20true%20%3F%20'btn-warning'%3A%20'btn-success'%7D&p4=%2C%duplicatesInList%20%3D%3D%3D%20true%20%3F%20'btn-warning'%3A%20'btn-success'%7D

Pretty weird for me. SOLUTION:

ng-class="duplicatesInList === true? 
'btn btn-warning pull-left': 'btn btn-success pull-left'"

Codes in answers also works (and IMO are a little better wrote than my solution:) )

Answer 1

<button ng-class="{
    'btn pull-left' : true,
    'btn-warning' : duplicatesInList,
    'btn-success' : !duplicatesInList
    }"
id="saveScoreButton" type="button" ng-click="add()"><button>

Answer 2

An alternative solution is,

<button class="btn pull-left" 
ng-class="duplicatesInList ? 'btn-warning': 'btn-success'"
id="saveScoreButton" type="button" ng-click="add()"></button>

Answer 3

Here's a working example:

Html:

<div ng-app='myApp' ng-controller='testCtrl'>

<button ng-class="{
    'btn-pull-left' : true,
    'btn-warning' : duplicatesInList,
    'btn-success' : !duplicatesInList
    }" id="saveScoreButton" type="button" ng-click="add()">Here</button>
    </div>

CSS:

.btn-pull-left
{
    float:left;
}

.btn-warning
{
    color:blue;
}

.btn-success
{
    color: green;
}

JS:

angular.module('myApp',[]).
controller('testCtrl',function ($scope){
    $scope.add = function(){
        $scope.duplicatesInList = !$scope.duplicatesInList;
    }
});

And the most important -> FIDDLE.