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>